356 



MOLLUSC A. 



are fertilised. The second structure associated with the 

 female duct is a conspicuous mucus gland, formed of two 

 sets of finger-like processes. The mucus secretion of this 

 gland is very abundant during copulation, and as it contains 

 not a little lime, it is possible that it may form the calcareous 

 shells of the eggs. 



(£) Finally, between the entrance of oviduct and penis 

 into the terminal aperture there lies a firm cylindrical 

 structure, larger than the penis and with muscular walls. It 

 is the Cupid's Dart Sac, and contains a pointed calcareous 

 arrow {spiculum amoris), which is jerked out previous to 

 copulation. The dart is sometimes found adhering to the 

 skin of a snail, and after copulation the sac is empty, soon, 

 however, to be refilled. 



When two snails pair, the genital apertures are dilated, 



bl.g c.p 



Fig. 1 1 6. — Diagram of larva of /'<z/2(«'/;;(!:. (After Erlangf.R.) 



Ec, ectoderm; £n., endoderm ; v. velum, with cilia; ^., gut 

 cavity; S.c, segmentation cavity; tr./., coslome pocket from gut; 

 Si.ff., blastopore groove closed, except at <^/. , which becomes the 

 anus. 



the protruded penis of one is inserted into the aperture of 

 the other, and the transference of a spermatophore is thus 

 effected. 



The eggs are laid in the earth in June and July. Each is 

 surrounded by gelatinous material acquired in the oviduct, 

 and by an elastic but calcareous shell. 



Segmentation is total but slightly unequal. As the snail 

 is a terrestrial Gasteropod, there is no trochosphere larva nor 

 more than a slight hint of the characteristic MoUuscan 

 velum. A miniature adult is hatched in about three weeks. 



