GONADS OF THE SNAIL 



445 



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• C. - - 



ally seen in Helix pomatia. A spermatophore from another 

 snail passes into the receptaculum, and is there dissolved 

 after some days, liberating hundreds of spermatozoa. By 

 these spermatozoa the ova of the snail are fertilised. It 

 seems likely that the place of fertilisation is in a small 

 diverticulum at the upper end of the oviducal side of the 

 common duct, whither the spermatozoa are said to find 

 their way. The second structure associated with the female 

 duct is a conspicuous mucus gland, formed of two sets of 

 finger-like processes. The secretion 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. It seems to 

 serve as a lubricant which 

 facilitates the expulsion 

 of a calcareous dart and 

 the copulation. 



{g) Finally, between 

 the entrance of oviduct 

 and penis into the ter- 

 minal aperture there lies 

 a firm cylindrical struc- 

 ture, larger than the penis 

 and with muscular walls. 

 It is the Cupid's Dart Sac, 

 and contains a pointed 

 calcareous arrow {spicu- 

 lutn amoris), which is jerked out previous to copulation. 

 The dart is sometimes found adhering to the foot of a 

 snail, and after copulation the sack is empty, soon, however, 

 to be refilled. 



When two snails pair, the genital apertures are dilated, the 

 protruded penis of one is inserted into the aperture of the 

 other, and the spermatophore of each snail is transferred 

 to the receptaculum of the other. 



The large 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 



Fig 



Ec 



big c.p. 



254. — Diagram of larva of Palu- 

 dina. — After Erlanger. 



Ectoderm; En., endoderm ; V., velum, 

 with cilia ; g., gut-cavity ; S.c, segmenta- 

 tion cavity ; c.p., coelom pocket from gut ; 

 bl.g., blastopore groove closed, except at 

 bl., which becomes the anus. The origin 

 of the mesodenn from a gut-pocket is clearly 

 seen in Paludina. 



