1. Both kinds of young females, female-producing and male-producing, pair with male individuals and receive active sperm into their body cavities. 2. The young female-producing females having been injected with living sperm by the male mature and produce parthenogenetic daughter-females but the young male-producing females having been injected with living sperm by the male mature and produce thick-shelled fertilized eggs. 3. Male individuals pair and inject active sperm into the body cavities of each other. 4. The mature female-producing females and the mature male-producing females pair with male individuals but do not receive sperm into their body cavities because the copulatory organ of the male is unable to pierce through the thickened cuticle of the adult female. 5. Much of the sperm of the males may be wasted by being injected into young female-producing females or into other male individuals or by being shed into the water in attempted copulation with adult females.