To facilitate sexual reproduction, some of the gonidia of a Volvox colony may undergo repeated divisions that result in round or oval-shaped sperm packets. This process is believed by many to cause the colony to produce a pheromone that causes other Volvox colonies in the surrounding area to become sexually active. If accurate, the probability that the sperm packets will quickly find female Volvox colonies when they are released into the water is increased. Once an appropriate colony is located, the sperm packet enters with the help of enzyme secretions and, when inside, breaks up so that individual gametes are free to fertilize nearby eggs. It is important to note, however, that it is also possible for Volvox to produce both eggs and sperm packets in a single colony, enabling them to sexually reproduce without the involvement of other individuals. In either scenario, successful fertilization generally results in the formation of a resting zygote that features a thick, spiny cell wall that can withstand harsh environmental conditions.