488 THE INVERTEBRATA 



covering of the spermatophore is dissolved, and the spermatozoa set 

 free. These now retrace their path to the junction with the female duct 

 and then up that duct to the fertilization pouch. Fertilization takes 

 place in May or June but the eggs are not laid till July. It is said that 

 the foreign sperm remains in the pouch during this time, and that 

 immediately before ovulation the sperm produced by the individual 

 itself degenerates within the hermaphrodite duct so that the eggs pass 

 down the duct without any danger of being self-fertilized and meet 

 the foreign sperm at the end. After fertilization, the egg cell passes 



wgr...^ 



lat. 



cent. 



K!.^^ 



Fig. 362. Radula of various types. A, Docoglossate (Patella). Stout teeth 

 used for rasping encrusting layer of algae off rocks : radula of relatively 

 enormous length; the teeth are quickly worn away. B, Rhipidoglossate 

 (Haliotis). Lateral and central teeth as in Patella, used in browsing on algae 

 growing on stones. The marginals, of which only about half are shown, are 

 probably used as a sieve to prevent fragments of food of too great size entering 

 the oesophagus. C, Rachiglossate (Buccinum). Teeth of carnivorous type, 

 with sharp cusps. D, Toxiglossate (Conus). Specialization of carnivorous 

 type, in which only two teeth (laterals) remain in each row, are hollow, and 

 are used as poisoned daggers, carrying the secretion of the salivary glands. 

 cent, central, lat. lateral, ??ig. marginal teeth. 



down the oviduct where it is enveloped with such quantities of 

 albumen that the diameter of the albumen envelope is 20-30 times 

 that of the egg cell itself. In the outer layer of albumen a skin appears, 

 and in this crystals of calcium salts are laid down which aggregate to 

 form a definite shell. The eggs are laid in July and August in small 

 holes in the earth and hatch after about twenty-five days of develop- 

 ment. 



In the autumn the snail loses its appetite and hides, often in 

 company with large numbers of its fellows, under leaves, making a 

 small hole in the ground with its foot and shell in which it lies with 



