Thin unstained, transparent specimens are excellent candidates for imaging with classical differential interference (DIC) microscopy techniques over a relatively narrow range (plus or minus one-quarter wavelength) of bias retardation. The digital images presented in this gallery represent a wide spectrum of specimens, which vary from unstained cells, tissues, and whole organisms to both lightly and heavily stained thin and thick sections. In addition, several specimens exhibiting birefringent character are included to demonstrate the kaleidoscopic display of color that arises when anisotropic substances are imaged with this technique.

American Dog Tick (Dermacentor variabilis) - The American dog tick is a member of the hard tick family Ixodidae. Hard ticks are responsible for transmitting nearly all of the major tick-borne diseases in North America. Though generally not believed to be vectors of Lyme disease, American dog ticks are the primary carriers of the Rocky Mountain spotted fever bacterium Rickettsia rickettsii. They are also capable of transmitting tularemia, Colorado tick fever, and anaplasmosis, and may cause paralysis when a neurotoxin they produce is secreted into a host's blood stream.

Amphipods (Grammarus) - Approximately 4,600 species of amphipods exist, but they are often known by other names. Amphipods that live in sandy beaches are frequently called sand hoppers or sand fleas, while those that thrive in freshwater habitats and marine beaches are commonly referred to as scuds. Yet, no matter what name they are known by, most amphipods are brightly colored and are similar in appearance to petite shrimp, generally ranging in size from four to ten millimeters. In the deep sea, however, some scavenger species of amphipods may obtain lengths of up to 140 millimeters.

Ancylostoma Hookworm - Hookworm infestation is known as ancylostomiasis and serious cases can result in as much as 200 milliliters of blood loss per day. The condition tends to be most prevalent in tropical regions and may affect animals, such as dogs and cats, as well as humans. Symptoms of ancylostomiasis vary by host, but often include diarrhea, weight loss, and severe anemia. In fact, during the late 1800s an epidemic referred to as miners' anemia occurred among Italian laborers building the Saint Gotthard railway tunnel in the Swiss Alps. The hookworm species Ancylostoma duodenale was responsible for the outbreak.

Aurelia Jellyfish (Strobila Stage) - Primarily found in coastal waters, the mature marine invertebrates may grow as large as 40 centimeters in diameter. Their medusoid bodies are bell-shaped, but some species lack the long, stinging tentacles frequently associated with jellyfish. In fact, Aurelia aurita, better known as the moon jelly, has tentacles so small that few notice them on first sight. Close inspection reveals, however, numerous short, fine structures lining the bell margins of the organisms. Since their tentacles are not well suited for capturing prey, moon jellies often ensnare zooplankton with the mucus that covers their outer surfaces, transporting the food to their mouths with the help of cilia.

Canine Tapeworm (Echinococcus granulosus) - The mature E. granulosus worm consists of three to five segments, generally reaching approximately five millimeters in length. The scolex of the organism is globular in shape and features a prominent projection known as a rostellum that is lined with a double row of hooks. The hooks enable the parasite to firmly lodge itself into the tissues of its host. The eggs produced by the adult parasites and expelled from the definitive host with bodily wastes are extremely resilient, surviving for up to a year even in very poor environmental conditions. Over that time, suitable intermediate hosts may accidentally consume them, which allows the parasitic lifecycle to continue on unabated.

Cat Testes Stained Thin Section - Members of the family Felidae, cats are carnivorous and are highly reputed for their hunting abilities. In fact, their finesse at capturing fish, birds, and rodents played a large part in their domestication and their early sacred status. Also, when cats became unpopular in Europe and their numbers decreased, the flourishing of rat populations that resulted helped lead to the spread of a great number of plagues and epidemics. By the seventeenth century, Europeans began to realize their mistake and cats became accepted household companions once again. Yet, even in modern times, vestiges of their former persecution remain, as is evidenced by the continued association of black cats with Halloween and bad luck.

Chicken Embryo - In the laboratory, chicken embryos and cultured cells are of great use to scientists. Most chickens have genes that are similar to those found in humans and, therefore, chicken cells may be utilized to achieve a better understanding of human biology and mammalian development in general. Chicken embryos are normally better suited to controlled studies than other laboratory animals, such as mice and rats, because they develop inside an egg rather than in the body of the mother. In fact, the relatively recent increase in the scientific use of chicken embryos may help reduce animal testing by replacing exposure trials on mice and rats.

Chicken Embryo Lens - Although initially all cells within a chicken embryo look alike, they quickly begin to develop into specialized structures. Within the first 24 hours of embryonic development, the head becomes distinguishable, the foregut forms, blood begins to accumulate in areas that will become parts of the vascular system, and the eye starts to take shape. Developmental progression moves swiftly, and on the second day the lenses of the eyes materialize, the vascular system takes a definite form, and the heart begins beating. The lightning-fast pace of growth and change continues, each feature developing within a set period of time, until a few short weeks later a full-formed and functional baby chicken, complete with claws and feathers, taps it way out of its shell to first see the light of day.

Chinese Liver Fluke (Clonorchis sinensis) - Similar to many other parasites, Chinese liver flukes have a three-host lifecycle and must, therefore, reside in two intermediate hosts before infecting a definitive host. The first hosts of the species are snails, which ingest the eggs of the flukes from contaminated water. The eggs complete their gestation in the snails before hatching and exiting the organisms. The trematodes then burrow into fish, their second intermediate hosts, where they become encysted inside muscle tissue. Humans, or other animals, become the final hosts of the flukes when they eat the raw flesh of an infected fish.

Chironomid Fly Larva - The metamorphic lifecycle of a chironomid consists of several phases, including egg, larval, pupal, imago, and flying adult stages. It is only in their larval form that the flies can feed, so during that time they must consume enough nutrients to last them the rest of their lives. Worm-like in appearance, chironomid larvae typically inhabit the sediments of freshwater bodies where they feed upon algae and other small organisms. They may also exist, however, in marine or terrestrial environments. One unusual species, aptly nicknamed the ice worm, actually proliferates in the icy cold waters of New Zealand's west coast glaciers.

Commercial Sponge Fibers - Sponges do not naturally exhibit the fresh, golden appearance that they have when modern consumers buy them from stores. In fact, when divers first bring them up from the sea they are black and rather unpleasant. A systematic process of washing and pressing the sponges must be followed in order to break down their external membrane and tissues. When only the skeletal fibers of the creatures remain, they are trimmed, dried, and frequently immersed in a mixture of water and hydrochloric acid, a procedure that gives them a blonde coloring, before being sold by merchants.

Ctenoid Fish Scale - Three general types of ctenoid scales have been categorized, but each type is composed of two key sections; a rigid surface layer chiefly consisting of crystallized calcium salts and a deeper layer that is formed by collagen-type fibrils. The distinction between the ctenoid scale types, therefore, is primarily based upon their form. Crenate scales, for instance, feature simple indentations on their edges, while spinoid scales are characterized by a cluster of spines that extend from the main scale body. Basic ctenoid scales, on the other hand, exhibit ctenii, which are formed as separate bony growths distinct from the main body of the scale.

Cucumber Tapeworm (Dipylidium caninum) - Proglottids, which are actually closer in size and shape to grains of rice, are a primary indicator of cucumber tapeworm infection. They contain egg cases and may be found in the bodily waste of definitive hosts, such as canine and feline species and, occasionally, humans. Definitive host infection occurs through the accidental ingestion of a contaminated intermediate host, which may be either a flea or a louse. Adult lice and larval fleas become infected by swallowing eggs released from the proglottids of a mature cucumber tapeworm.

Cycloid Fish Scale - The primary types of fish scales include placoid, cosmoid, ganoid, ctenoid, and cycloid scales. Placoid scales, which consist of an outer layer of an enamel-like substance, an inner stratum of dentine, and a pulp cavity, are exhibited by sharks. Most primitive bony fish species, however, generally possess scales of ganoid or cosmoid type, which are thick and composed of several layers of bone, enamel, and related substances. Some advanced fishes also exhibit bony scales, but these typically allow more freedom of body movement than the earlier-evolved varieties. Thin, translucent, and lacking enamel as well as dentine, these modern structures are known as cycloid and ctenoid scales.

Deer Tick (Ixodes dammini) - Deer ticks have a complex, two-year lifecycle that consists of several stages. Eggs are generally deposited in the spring and tiny larvae emerge several weeks later. The larvae attach to small mammals, such as field mice, and feed before falling to the ground and overwintering. The following spring, the larvae molt into nymphs that feed on mice or larger mammals during the summer. It is in this stage that deer ticks are most likely to bite humans. After their blood meal, the nymphs molt again, achieving their adult form in the fall. Adult ticks normally attach themselves to white-tailed deer, or other large mammals, to mate. Afterwards, males fall from the host and die, while females feed once more in order to successfully produce eggs.

Desmid Algae - Since they are so small, the beauty of desmids tends to go unnoticed unless they are examined through a microscope. Strikingly symmetrical, each individual desmid is divided into two mirror-image halves, or semicells, which are connected by an isthmus that contains the nucleus. The semicells may be globular, disc, spindle, or crescent shaped, and can feature a cell wall ornamented with spines or spectacular patterns of granules and tubercles. Desmids have an even more unusual appearance when they are in the process of dividing. During this time, two new semicells are created in between the old semicells, often remaining attached for a short period.

Diatom Frustule - Diatoms are unicellular phytoplankton that may be found in all of the Earth's aquatic environments. However, most species occur solely in areas that meet specific physical, chemical, and biological requirements. This habitat specificity is frequently utilized by ecologists to ascertain the state and quality of a body of water. Furthermore, the extensive fossil record of diatoms provides scientists with a unique historic record of changes in marine ecosystems.

Digenetic Trematode (Echinostoma) - The life cycle of digenetic trematodes is complex, involving one or more intermediate hosts and a primary host. The endoparasites of the genus Echinostoma often infect avian species, such as ducks, geese, and pigeons, as well as humans. These animals become contaminated by ingesting raw freshwater snails or frogs that act as intermediate hosts of the trematodes. In their final adult forms, the flatworms use oral and ventral suckers to hold onto the lining of the bird cecum or human rectum. Since these hermaphroditic flukes cannot biosynthesize their own fatty acids and sterols, they must depend on parasitism to fulfill their nutritional needs.

Down Feathers - There are three basic types of feathers, each with its own set of specific functions. Contour feathers line the wings, tails, and backs of birds, giving them a defined shape and acting as aerodynamic structures. Beneath them, lie the soft, fluffy feathers commonly referred to as down. As anyone who has ever used a down comforter or sleeping bag should know, down feathers are excellent insulators. Thus, their primary function is to maintain the proper body temperature of birds, a task that they are aided in by hair feathers. Sometimes alternatively known as filoplumes, hair feathers are also believed to function as pressure and vibration receptors that sense the location of other feathers so that they can be appropriately adjusted.

Earthworm Muscle Tissue - Earthworms vary in length depending upon species and belong to the phylum Annelida, which contains the segmented worms. The common earthworm Lumbricus terrestris, known as the night crawler in the United States, rarely exceeds lengths of more than ten inches. However, some tropical species of earthworm can be up to eleven feet long. In order to move such long, tapered bodies forward, earthworms exhibit peristalsis, a wave-like motion achieved through rhythmic muscular contractions. With the additional aid of the setae that line each of their body segments, earthworms are relatively adept at wriggling their way through the soil and across the ground.

Earthworm Nervous Tissue - Earthworms do not have eyes or ears, but are perceptive of light and sound. This strange phenomenon is possible because the earthworm nervous system is connected to a variety of sensory cells that are capable of detecting different environmental factors. Earthworms also have a developed sense of touch, a sense of taste, and can perceive the amount of moisture in surrounding soil. Some studies have even shown that earthworms can store simple memories, such as which branch of a Y-shaped tube should be taken to avoid an electrical shock.

Euchlanis Rotifer - In addition to a ciliated corona, or head, Euchlanis species have transparent bodies and two strong toes used for swimming. They are also sheathed in a glassy shell secreted by their outer skin. Inside, each tiny individual rotifer is surprisingly complex, possessing a brain, bladder, reproductive organs, intestines, and a stomach. They are not endowed, however, with a circulatory system.

Fat-Stained Adipose Tissue - The body fat that human dieters are generally concerned about is stored in white adipose tissue. Excessive body fat can lead to health problems, but a certain amount of white adipose tissue is necessary for the proper functioning of the body. In addition to storing energy, the tissue, which is usually located directly below the skin, protects the body from impact-related damage to the organs and acts as a heat insulator. In addition to exercise and diet, there are a number of factors that have an apparent effect on the distribution and amount of white adipose tissue stored in a body, including gender, genetics, and race.

Fern (Polypodium) Leaves - More than 10,000 species of fern have been scientifically catalogued, some of which date back 360 million years ago to the Carboniferous period. Man has utilized the plants in various ways since he first began to walk on the Earth. Ferns, or parts of the ferns, have been used as a food source, as bedding and stuffing for cushions, as medicinal treatments, as material for roof thatching, and as ornamentals. Most recently, ferns have acted as a subject of study in biological research, scientists being extremely interested in their retainment of a primitive lifecycle that involves two separate, generally independent generations.

Frog Heart Muscle Tissue - Unlike most mammalian species, frogs and other amphibians possess nucleated blood cells, which is an indication of their less evolved nature. Moreover, their circulatory systems feature a heart that has only three chambers, rather than the four possessed by humans and other more advanced species. The combination of two atria and a single ventricle complicates circulation because blood returning to the heart from the lungs is combined with incoming blood from the body, resulting in mixing between oxygenated and deoxygenated blood. Frogs handle this situation, however, by having a very slow metabolism and by absorbing some oxygen through their skin. There is also some directional control of the distribution of blood flow by the ventricle.

Frog Testes (Meiosis) - Typically, male frogs desiring to breed use mating calls to attract females, who are able to differentiate their own species based on the sound and location of the call. When a potential mate arrives, the male clasps her from behind in a copulatory embrace known as an amplexus. Sperm is ejected onto the eggs as they are released by the female. The eggs, which vary in number depending on species, then float or sink in the tranquil water until they eventually hatch into tadpoles.

Fungus (Sordaria fimicola) Fruiting Bodies - Ascomycetes are known as sac fungi because of the characteristic shape of their asci, which each contain four to eight ascospores in the sexual stage. The specific attributes of the asci and the method of release of the ascospores is what primarily determines which subgroup ascomycete species are placed in. Other differences do exist between the fungi, however, which may follow very different paths of existence. Some ascomycetes are pathogens that cause disease in plants or animals, while others are edible or harmlessly live on dead organic matter. Perhaps the ascomycete most important to man is Saccharomyces cerevisiae, the common yeast that is used around the world to leaven bread and ferment the grain that produces beer.

Human Cerebrum - Modern science has revealed that the human brain is divided into several sections that work together to complete the complex functions of humans. The three primary regions of the brain are the brain stem, the cerebellum, and the cerebrum. The cerebrum is currently the largest part of the human brain, comprising approximately 85 percent of its total weight and weighing almost three pounds. The cerebrum of early man, however, was not as developed as it is today, encompassing only about a third of its current weight. Thus, as the composition of the brain has changed dramatically over the last 100,000 years, so have the mental processes of humans.

Human Cheek Epithelial Cells - Cheek cells are often studied in school laboratory settings because they can be easily obtained through a mouth rinse or simple swab. Yet, though the individual cells appear very simple under the microscope, they each contain the genetic make-up of the entire body. Thus, they are often used for DNA fingerprinting studies, as well as paternity testing. Interestingly, a group of Australian researchers have recently found another use for human cheek cells. They have devised a test that utilizes cheek cells to measure an individual's proclivity for high blood pressure.

Human Erythrocytes - Human erythrocytes generally only live for about 100 days and, therefore, must be periodically replenished. The majority of new erythrocytes develop in the bone marrow through a several stage process and are stored in the spleen. Beginning as a hemocytoblast, a cell that has multiple development potentials, in the mesenchyme, the structure slowly turns into an erythroblast, which then loses its nucleus and mitochondria and gains hemoglobin. A later stage of the cell known as a reticulocyte, is what finally develops into an erythrocyte. The entire progression from hemocytoblast to red blood cell requires two to five days to complete.

Human Flea (Pulex irritans) - The human flea is mainly a nuisance, an enzyme in their saliva producing an allergic reaction in their victims that causes an itching sensation. However, the parasite can also be a vector of a variety of diseases. Though it was not the primary species responsible for spreading the bubonic plague throughout Europe during the Middle Ages, the human flea is capable of transmitting it. The species may also transmit murine typhus, tularemia, and tapeworm, but such occurrences are relatively rare.

Hydatid Cyst - Hydatid cysts are typically spherical in shape and have the ability to achieve rather large sizes. The insides of the cysts are filled with fluid, brood capsules, daughter cysts, and protoscolices that have the capability to grow into adult worms if consumed by a definitive host. If a cyst is ruptured, which may occur through a sharp blow or during surgery, each protoscolex released may form a new cyst. Also, the fluid within the hydatids is highly allergenic and may cause anaphylactic shock and rapid death if freed inside the body.

Indian Muntjac Deer Skin Fibroblasts - Generally solitary creatures, muntjacs can be extremely competitive. Males frequently fight over mates and territory, using their antlers and canine teeth, which are elongated into tusks, as weapons. Although they are diminutive in size, they are capable of inflicting serious injuries to other animals. They cannot easily defend themselves against humans, however, and are often hunted for their skins and meat. Thus, some species of muntjacs are endangered, although the Indian muntjac appears to remain relatively abundant.

Intestinal Fluke (Heterophyes) - Humans and other mammals become infected with the digenetic trematode by eating contaminated raw or undercooked fish. Thus, most cases of heterophyiasis occur in the Far East, the Middle East, and Egypt due to the characteristic diets of inhabitants of these areas. True levels of incidence are difficult to discern, however, because cases are often asymptomatic and signs of serious occurrences, such as abdominal pain, diarrhea, and the frequent appearance of eggs in feces, are similar to those of other types of parasite infection. In rare instances, H. heterophyes can cause the lining of the small intestine to break down, and the eggs produced by the parasite enter into the blood stream. Once in the blood stream the eggs may be carried to other organs where they can instigate acute medical problems.

Intestine Thin Section - In humans, the most prominent structure of the digestive system is the small intestine, which is generally more than 20 feet long. In nonhuman primates, however, the large intestine is a more central component to the digestive process. This divergence between humans and creatures such as gorillas and orangutans reflects the vast differences in their diets. As omnivores, humans generally consume high quality foods that contain significant amounts of protein, fats, and carbohydrates. The slower moving, nonhuman vegetarian primates, however, eat lower quality plants that contain a higher proportion of roughage.

Jellyfish Sensory Organs (Aurelia Tentaculocysts) - One of the jellyfish most familiar to humans is the moon jelly, scientifically known as Aurelia aurita. The species is easy to recognize because of the four round, or horseshoe-shaped, reproductive organs that can be clearly seen through their transparent pink or bluish hued bodies. The tentacles of moon jellies are short and fringelike, and their sting is much less toxic than many other types of jellyfish. Also, the stinging action of their nematocysts is not powerful enough to pierce the thick skin of humans, though they can occasionally catch small aquatic animals. Most of their food is instead gained by trapping plankton in the layer of mucus that coats their bells.

Kapok Fibers - In order to prepare kapok fiber for export, the material is removed from the pod by hand and then dried and separated from the seeds. Though too brittle and inflexible to be spun into thread, importers have found other uses for the substance. Since kapok fibers are cellulose tubes that contain a small quantity of air, they are extremely buoyant and can support up to 30 times their own weight in water. The material, therefore, is often used in life preservers and other water-safety gear. Due to its other commendable qualities, such as its non-allergic, non-toxic, and odorless nature, kapok fiber is also popular for stuffing items like pillows, mattresses, and sleeping bags.

Kevlar Fibers - Sometimes referred to as a Space Age material, it is the chemical structure and processing of Kevlar that makes it so strong. More specifically, Kevlar contains both aromatic and amide molecular groups. When molten Kevlar is spun into fibers at the processing plant, the polymers produced exhibit a crystalline arrangement, with the polymer chains oriented parallel to the fiber's axis. The amide groups are able to form hydrogen bonds between the polymer chains, holding the separate chains together like glue. Also, the aromatic components of Kevlar have a radial orientation, which provides an even higher degree of symmetry and strength to the internal structure of the fibers.

Lancelets (Amphioxus) - Amphioxi, which are also often referred to as lancelets, are invertebrates that were mistaken for slugs when they were first discovered in 1778 by Piotr S. Pallas. The misidentification is understandable since the marine animals have tapered forms without eyes or distinct heads. The creatures also do not have well developed brains or hearts and are not buoyant. They can swim side to side by contracting the staggered muscle blocks that line the flanks of their bodies, but whenever they cease to do so, they sink.

Lancelet (Amphioxus) Pharynx - Though capable of swimming, lancelets typically remain buried in the sand or mud that lines the ocean floors. To feed, they extend the anterior portion of their bodies upward out of the muck and the cilia that line their gill slits direct water toward their mouth openings. From the mouth, the water moves into the pharynx, the mucous membrane of the gill basket capturing edible organisms in the water and passing them onto the gut, where digestion begins with the aid of various enzymes. Unlike other chordates, lancelets are capable of phagocytosis, a digestive process in which individual cells consume food particles.

Lily Flower Buds - Herbaceous flowering monocots, lilies are usually raised from bulbs and grow best in loamy soil. Although the belief in their medicinal value seems to have been unfounded, the plants were used for many years to treat fever, rheumatism, and arthritis, as well as to clean wounds, burns, and sores. Such medical applications of lilies were especially popular in England during the Elizabethan period.

Lone Star Tick (Amblyomma americanum) - Many animals are potential hosts for the lone star tick, which needs three blood meals in order to develop into its adult form. In their immature stages, the ticks prefer to feed on birds and small mammals, though they may also feed on larger animals. Bovines and white-tailed deer are favorite hosts of fully mature lone star ticks. All life stages of the creatures, however, will feed on humans as well.

Mammalian Liver Thin Section - Essential to life, the liver, which is susceptible to many diseases and infections, can lead to serious medical problems if it is damaged. One of the most obvious signs of liver impairment is the yellowing of the skin and eyes known as jaundice. Jaundice may occur from a variety of liver malfunctions and, therefore, tests must be carried out to make an accurate diagnosis. In many instances of liver damage, as in cases of cirrhosis or hepatitis, bed rest and complete avoidance of alcoholic beverages may result in a remarkable improvement of health.

Moss Antheridia - In the gametophyte form of mosses, reproduction is generally sexual and is seasonally controlled. Male sex organs known as antheridia and female sex organs, which are referred to as archegonia, are typically located at the tips of the main shoots of gametophyte mosses. Whether shoots are unisexual or bisexual is a species dependent characteristic, but many mosses are designed to discourage inbreeding. The reproductive process itself can only take pace when the plant is wet, sperm released from antheridia swimming to female archegonia to penetrate ova and create a zygote.

Moss Bulbils - Wide distribution of mosses has played an important part in making Earth inhabitable for more advanced life forms. Mosses have existed for more than 200 million years, appearing sometime after the algae and fungi. The mosses survived in the small amount of nutritive soil that was formed by the decaying material of the more primitive plants, breaking down exposed substrata and releasing nutrients. The remnants of dead mosses then created an even thicker layer of rich soil, making it possible for more complex plants to grow on the surface of the planet.

Mouse Kidney Thin Section - The close mammalian relationship between mice and humans means that many of their organs function in the same way, even though they may vary in size or location. The kidneys, for instance, maintain water balance and expel metabolic wastes in both species. They also have a similar appearance; bean shaped, brownish red, and granular. The outer region of both human and mouse kidneys is called the cortex and the inner area is known as the medulla. Nephrons, which are the functional units of the kidneys, stretch across both sections and are responsible for filtering blood, reabsorbing water and nutrients, and secreting wastes.

Mushroom (Polyporus) Fungus - Several varieties of fungus are associated with mushrooms, although many of them are not safe to eat. In fact, poisoning by wild mushrooms is a fairly common occurrence and can be fatal. Thus, it is extremely important that all mushrooms that are to be eaten are first clearly identified. Some prominent cases of mushroom poisoning, however, may have been intentional. The Roman emperor Claudius, for instance, is often said to have died in 54 AD from eating a dish of poisonous mushrooms given to him by his ambitious wife and niece, Agrippina, who wanted her son Nero to rule.

Nucleic Acid Stains - In modern times, the process of staining cells to observe their features is widespread, and scientists have an array of stains, generally composed of heterocyclic organic dyes, to choose from. In order to make a suitable stain selection, the chemical and electronic properties of the dye molecules with respect to their interaction with cellular components must be considered. For instance, stains that have a net positive charge in aqueous or buffered solutions have an affinity for negatively charged biological structures and selectively bind to them. Hydrophilic stains, on the other hand, tend to stain hydrated biological bodies, such as the exterior of proteins and nucleic acids. Contrariwise, stains hydrophobic in nature concentrate on membranes, lipids, and the interior of proteins.

Obelia Hydroid - The polyp members of Obelia are asexual, stalk-like, and usually attached to the ocean floor, rocks, shells, or other surfaces. The polyps generate additional polyps by budding, creating a branching colony of the organisms that has a structure similar to that of a tree. A transparent sheath known as the perisarc encases the colony. Dimorphic, some of the polyps are responsible for feeding, while others concentrate their energy on reproduction. The feeding polyps feature tentacles and share the nutrients they imbibe with the rest of the colony after digestion in the gastrovascular cavity. Reproductive polyps, however, lack tentacles and are club-shaped.

Pennaria Hydrozoa - Many hydrozoan species exist in colonies that are formed by the asexual budding of members. Generally, the buds in the colonies remain attached to the parent polyp, but some specialized reproductive polyps may produce free-swimming medusae. Hydrozoan medusae are bell-shaped and propel themselves forward by alternately constricting and relaxing muscles, which causes water to shoot out of a constricted opening in their bodies.

Pine Tree Pollen - Pollen is generally released by pine trees in the spring or early summer. The substance has the appearance of a fine yellow or green dust, and when it covers large areas, it is sometimes mistaken for a chemical spill. However, though pollen may cause allergic reactions in humans, it is for the most part harmless, and even beneficial to some species. In fact, pine pollen acts as a source of food for a variety of fungi and microscopic animals.

Planaria Cross Section - Planaria are generally carnivorous night feeders that consume aquatic insects, snails, microcrustaceans, and proteinaceous detritus, though a few species are parasitic. The mouths of the flatworms are located on their ventral side more than halfway toward the tail, an opening through which they may extend the pharynx. Typically, enzymes secreted by the mouth partially digest prey while it is pinned outside the body by the pharynx. Once softened, the mouth sucks in the food and digestion continues within a three-branched gastrovascular cavity.

Polypropylene Fibers - Polypropylene fiber has many positive characteristics that dictate its wide range of applications. The material is strong, quick drying, colorfast, stain resistant, thermally bondable, and hardy against chemicals, perspiration, mildew, and weather conditions. Moreover, polypropylene fiber has the lowest specific gravity of all synthetic fibers, which makes it lightweight and enables it to float in water. Due to such qualities, the material is used in an array of items, including baby diapers, hygiene products, sportswear, carpeting, upholstery, ropes, and automotive interior fabrics. Also, recently polypropylene fiber has become a common additive in concrete, believed to be an effective method of controlling shrinkage cracking.

Portuguese Man-of-War Tentacles - The dreaded tentacles of the Portuguese man-of-war belong to the dactylozooid polyps it contains. Their stinging nematocysts can paralyze small prey and cause immense pain to humans, which is sometimes accompanied by powerful allergic reactions that lead to fever and shock, as well as heart and lung problems. In fact, the toxin exuded by the tentacles of the Portuguese man-of-war is about 75 percent as powerful as the venom of a cobra. Even when they are washed up on the beach, the tentacles remain dangerous and should not be touched with bare skin.

Ragweed Pollen - Approximately fifteen species in the genus Ambrosia are commonly referred to as ragweed. The plants feature rough stems, small yellow-green flowers, and lobed leaves. They often grow in disturbed soil that cannot support other types of vegetation and flourish in conditions of low humidity and high heat. In North America, ragweed is most abundant in the midwest and central United States, but few areas are free from it altogether. However, Portland, Oregon and Seattle, Washington, which claim that they do not have ragweed seasons, could be considered safe havens for hay fever sufferers.

Rocky Mountain Wood Tick - The lifecycle of the Rocky Mountain spotted wood tick generally takes two to three years to be completed and requires the parasitism of three different hosts. After each blood meal, the tick drops to the ground and molts into its subsequent form, or dies if it has already successfully completed the mating process. To find an appropriate host, the Rocky Mountain spotted wood tick climbs grass, bushes, and other foliage, where it waits for chemical cues that indicate the presence of a mammal. The parasite then drops itself onto the mammal and briefly moves about before attaching its mouthparts to the host's skin.

Silver Stained Human Cerebellum - In humans, the cerebellum is a peach-sized, lobed structure located near the base of the brain. It is primarily involved in controlling bodily movement and the development and recollection of physical skills. In order to function properly, the cerebellum must receive information from several parts of the body, such as the eyes, the ears, the limbs, and the cerebrum. The cerebellum, the name of which means "little brain" in Latin, then coordinates all incoming information and makes fine adjustments in motion at the subconscious level. This is how good tennis players can meet the ball in the right place at the right time and return it with appropriate force without having to willfully consider the motions of their muscles.

Spirogyra Filamentous Algae - More than 400 species of Spirogyra are known to be in existence and most are found free-floating in freshwater environments. The algae are particularly abundant in nutrient-rich environments and large populations can be an indication of over-fertilization caused by contaminated storm water. At night or when it is overcast, it may be difficult for the casual observer to determine the level of algae in a pond or other body of water. However, on sunny days, oxygen bubbles produced during photosynthesis cause Spirogyra to rise to the surface of the water, often in thick, tangled mats.

Sponge Skeleton - Sponges do not naturally exist in the soft, golden form that they exhibit on the shelves of modern bath stores. In fact, sponges grow in a wide array of shapes, sizes, and colors. Some varieties are as small as coins, while other may grow several feet in height. Sponges may be flat, smooth, branching, rough, soft, or prickly. They may also be shaped like cones, spheres, or tubes and colored red, yellow, green, blue, or almost any other color imaginable. Some of the pigments, however, are a result of algae that inhabit the inside of the sponge or that have been consumed by it.

Stained Chinese Liver Fluke Eggs - Adult members of the species reside in the bile ducts of the liver, generally growing to lengths of approximately one inch. They may live for more than 20 years and can produce a prolific number of eggs, as many as 4,000 in a single day. The eggs have a characteristic flask-like shape that features a prominent operculum at one end and a spine at the opposite extremity. They are passed through the intestines and are voided from the body with feces. Though the miracidium held inside the eggs is already well developed at this point, it does not hatch until it is ingested by an intermediate snail host. When their gestation is complete, the newly formed trematodes exit the snail and burrow into fish, where they encyst inside muscle tissue.

Stained Hydra - Often hermaphroditic, hydras may alternatively produce offspring sexually. Eggs and sperm are stored in separate swellings in the outer body layer of individual hydras. Fertilization occurs in the water after gametes of opposing sexes are released by two different hydras. The young embryos then attach to the hydra from which the eggs were donated and stay there until their mouths and tentacles develop. Subsequently, the new hydras break away from their mother to carry out the rest of their lives autonomously. Hydras generated in this manner tend to be better suited to surviving harsh environmental conditions than their asexually produced brethren.

Sun Animalcules (Actinosphaerium Heliozoans) - Heliozoans are generally freshwater creatures and can frequently be found in lakes and ponds. Depending on conditions and food supplies, areas may contain large populations, the heliozoans quickly reproducing asexually through binary fission or budding. Suitable food sources for the organisms include algae, protozoans, and other tiny life forms. However, heliozoans generally will try to consume most anything that comes across their paths since they have little locomotive ability.

Taenia Tapeworm - The lifecycle of tapeworms can be complex and may involve multiple hosts, but their anatomy is simple. Species either consist of a single segment or of a succession of identical segments called proglottids and a definite head, known as a scolex. The scolex lacks a mouth, but features suckers and often hooks which are used to attach to the internal organs of a host. Tapeworms also possess a simple nervous system, though they do not have a digestive tract and must absorb nutrients directly from an external layer of tough cuticle. The creatures are typically hermaphrodites and may produce offspring independently.

Timothy Grass Pollen - Sometimes referred to as herd's grass, timothy typically grows about three feet high and features non-branching panicles, or clusters of flowers. Each dense panicle is about 2 to 3 inches long and cylindrical in shape. The stems of timothy grass generally grow in large tufts and exhibit distended, bulb-like bases. The vascular plants also tend to shed large amounts of pollen and primarily pollinate in the morning hours of late spring or early summer, depending on geographical location.

Trematode (Fasciolopsis buski) Rediae - Humans become infected with F. buski, a condition known as Fasciolopsiasis, by consuming uncooked aquatic vegetables, such as lotus, water chestnuts, and water bamboo, contaminated with metacercariae. Generally settling in the duodenum, the metacercariae become adult worms in approximately 3 months. Though infection is sometimes asymptomatic, at the site of attachment deep inflammatory ulcerations often occur, usually accompanied by nausea, abdominal pain, and diarrhea, alternated with periods of constipation. Particularly large populations of F. buski can also involve mucus discharge, general body weakness, and fluid retention that may result in severe consequences if left untreated.

Triacetate Fibers - Derived from cellulose, triacetate is formed by combining cellulose with acetate from acetic acid and acetate anhydride. The cellulose acetate is then dissolved in a mixture of methylene chloride and methanol for spinning. Spinning, the oldest method of preparing man-made fibers, involves pumping a viscous polymer solution through a filter and subsequently passing it through the tiny holes of a spinnerette. Afterward, the solvent is removed and only a synthetic fiber remains.

Tubifex Worms - Tubifex worms are capable of thriving in oxygen-poor environments, such as sewage treatment ponds, because they possess a much more efficient manner of assimilating dissolved oxygen than most other organisms. The worms, which generally range in length from 1 to 8.5 centimeters, reside in mud tubes that they create out of a mixture of mud and mucus. However, they often leave their posterior segments outside of the tubes, waving them about and creating a current that enables them to collect any surrounding trace amounts of dissolved oxygen.

Vas Deferens Thin Section - The primary target of most permanent or semi-permanent types of male contraception is the vas deferens. The traditional vasectomy, for instance, involves the severing and sealing of each of the reproductive tubes. The surgical procedure is considered safe, simple, and may be completed by most physicians in less than 15 minutes. However, an even more refined method has been developed. Many doctors now offer a less invasive, no-scalpel method of vasectomy that has helped increase the acceptance of male sterilization in many parts of the world where conventional vasectomies were not highly regarded.

Vorticella Ciliates - Though they are frequently present in groups, each vorticella possesses its own unciliated stalk. The stalk enables the organisms to attach to aquatic plants and animals, submerged objects, or surface scum. A contractile fiber known as a myoneme is contained within the stalk, causing it to coil up like a spring when it is stimulated or disturbed.

Water Flea (Daphnia) - Generally, Daphnia are filter feeders that consume microscopic particles from surrounding water, though a few species are predatory. The small creatures are a significant and ubiquitous link in the food chain, serving as fare for many larger animals, including several important commercial varieties of fish. Populations of Daphnia are produced parthenogenetically most of the year, but in stressed conditions they may also reproduce sexually. The fertilized eggs that result are resilient and can overwinter, withstanding freezing or drying conditions until better circumstances indicate that it is time to hatch.

Whipworm (Trichuris) Eggs - The sole cause of whipworm infection is ingestion of Trichuris eggs. The eggs, which are expelled by infected individuals with bodily wastes, are quite resilient, however, and may survive in soil or on other surfaces for significant periods of time. When a suitable host ingests an infective egg, it hatches in the small intestine and the juvenile worm migrates to the large intestine. There the parasite embeds its anterior end into the intestinal lining where it reaches sexual maturity and remains for the rest of its lifecycle, which may be several years long.

Wild Silk Fibers - An animal fiber, most commercial silk is produced by the caterpillars of several moth species belonging to the genus Bombyx and are commonly referred to as silkworms. Virtual eating machines, cultivated silk worms can increase their body size up to 10,000 times their original dimensions in less than a month. When they are ready, they begin cocooning and extrude a semi-liquid mixture of protein and a sticky substance known as sericin. Hardening upon exposure to air, this liquid silk becomes the fiber that enshrouds them from the outside world while in their cocoon.

Zygnema Filamentous Algae - Capable of proliferating in several different ways, reproduction of Zygnema species is primarily dependent upon environmental conditions. When nitrates and phosphates are readily available, Zygnema generally reproduce vegetatively by fragmenting to create new strands. However, when conditions are less favorable, Zygnema often asexually produce akinetes, spore-like bodies that have very thick cell walls that enable them to survive harsh conditions. In poor environments, members of the genus may also reproduce sexually to create a zygospore that sinks into the sediment at the bottom of the body of water, where it waits to emerge until more propitious circumstances arise.

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