Four combinations of photoperiods and temperatures have been tested on the reproduction and on the activity of the genital apparatus of the snail Helix aspersa. The results show some interaction between photoperiod and temperature and reveal a predominant effect of photoperiod that compensates for the negative effect of low temperatures. A combination of long day (LD, 18L:6D) and a temperature of 20 degrees C is the most favorable condition for egg-laying as well as for the effective functioning of the ovotestis and albumen gland. In contrast, during a short day (SD, 8L:16D), egg-laying is completely inhibited at 15 degrees C and partly inhibited at 20 degrees C; the differentiation of gametes can be observed in the ovotestis, but the mature oocytes are not released and thus they degenerate. In the albumen gland, an important synthetic activity is noticed, but cellular multiplication and the release of the secretory products decrease. These results suggest that short photoperiods induce inhibition of the (neuro)endocrine centers responsible for the control of both ovulation and egg-laying.

Summary. The effect of lighting duration on the evolution of nurse cells and male line in the Helix aspersa ovotestis.Adult snails (Helix aspersa) were bred under two photoperiods i.e. long-day : 18 h (JL), short-day : 8 h (JC) immediately after a 4 month hibernation. In these conditions only the long-day snails began to lay eggs from the 10th week of experiment, whereas the others did not.To explain these differences, the structure and functioning of the hermaphroditic glands were investigated in both groups, 6 and 10 weeks later, using electron microscopic and quantitative biochemical methods.At 6 weeks, compared to short-day cycles (JC1, long-days (JL) highly increased spermatogonial multiplication measured by 3 H thymidine incorporation and on the other hand shortened the duration of spermatogenesis. Ultrastructural observations showed that modifications of the nurse cells were strongly correlated with the evolution of the male line.At 10 weeks, the rates of spermatogonial multiplication were rather similar in all snails.In spite of the absence of anomalies in the male cells, no reproduction occurred among the short-day animals ; this is probably due to a low concentration of sperm, suggesting an insufficient stimulation by the neuroendocrine controlling centers.Introduction.

Dormant, hibernating snails whose brains (supraoesophageal cerebral ganglia and associated dorsal bodies) were removed by surgery continued to live retracted in their shells. The remaining ganglia of the circumoesophageal ring did not regenerate in the 12 months following the removal of the brain. The transplanted brains in the haemocoel (auto- or allo-graft) were not rejected and many of their cerebral neurosecretory cells and the endocrine dorsal bodies appeared normal structurally and functionally, as evidenced by ultrastructural and immunocytochemical studies. The data from these experiments demonstrate the possibility of studying by in vivo culture methods the roles of cerebral ganglia and endocrine dorsal bodies on the control of reproduction under different temperature regimes.

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1. The results obtained after the removal of the supraesophageal part of the circumesophageal neural ring indicate that this part of the brain is involved in the control of spermatogenesis. In hibernating snails, when the supraesophageal ganglia are removed or disconnected from the subesophageal ganglia and from the cerebral sense organs, an increase in the rate of 3H-thymidine incorporation in the male sex cells in the gonad occurs. This suggests that while the supraesophageal ganglia impart an inhibitory influence on the DNA synthesis during spermatogenesis, the subesophageal ganglia stimulate it. 2. The microsurgical removal of different parts of the supraesophageal ganglia suggests that the mesocerebrum plays a major inhibitory role on spermatogonial multiplication. This inhibitory activity originates from groups of mesocerebral neurosecretory cells. These cells have cellular connections to the rest of the periesophageal nerve ring and with the endocrine cells of the dorsal bodies (DB). 3. The extirpartion of islets of neurons located near the cerebral commissure or the section of their axons which form synapse-like-structures with the DB induces an increase in the incorporation of 3H-thymidine by the male sex cells in the gonad. In hibernating adult snails these experiments indicate the inhibitory function of groups of neurons from mesocerebrum on DNA spermatogenic synthesis induced by an increase in temperature (5 to 25 degrees C). In the young snails, this area is the source of growth hormone.