Sexually mature female Schistosoma mansoni maintained in vitro without males laid eggs, a small percentage of which matured as evidenced by production of viable miracidia. The rates of oviposition and maturation of eggs were significantly increased by mating. Males made anorchid by X-ray, by prolonged in vitro maintenance, or by surgical transection mated and stimulated the rate of egg-laying and egg maturation as much as did intact males. Thus, neither mating, nor stimulation of the rate of oviposition depended on intact testes, viable sperm, or something secreted with sperm. Since anorchid males could not have donated sperm for the fertilization of eggs in females maintained in vitro, the feat must have been achieved by the sperm present in the female at the time of in vitro isolation. The decay rate of sperm in females maintained in vitro was found by allowing eggs laid on each day of days 1 through 5 of in vitro life to mature separately. This decay rate was exponential with time beginning on Day 2 of in vitro life. Stimulation of the rate of egg maturation by anorchid males was shown to be exponentially related to the rate of egg-laying. Therefore, the increase in the percentage of eggs which matured in vitro when females were mated to anorchid males, was due only to stimulation of the rate of oviposition by these anorchid males. The normal mating position of schistosomes is anterior end to anterior end, and posterior end to posterior end. Worms were transected into equal halves. When halves of worms were allowed to mate in vitro, like halves almost always mated normally and unlike halves almost always abnormally (more than 90% of the time for each type of mating). These observations were therefore not due to chance and require an explanation. From these results, and matings of halves of worms with whole worms of the opposite sex, and transections of males smaller and larger than halves with intact females, it was postulated that both sexes of worms have linear receptors which are used to determine mating and mating position. The receptors run at least throughout the posterior two-thirds of the male. They may be highly differentiated at their anterior and posterior ends, the anterior ending of the receptor in one sex being an inverse image of the posterior ending of the receptor in the same sex. When complementary receptors meet, mating position is normal; when noncomplementary receptors meet, mating position is abnormal. Attempts to determine the nature of these receptors by exposing living worms to enzymes were unsuccessful. © 1969.
