8o 



COMPARATIVE ANATOMY 



a transparent cuticular lens. The epithelium at the extremity 

 of the larger tentacles is further modified and provided with 

 numerous nerve end-organs, which have been proved to sub- 

 serve the function of smell. 



The auditory organs consist of a pair of otocysts embedded 

 in the pedal ganglia. They are innervated from the cerebral 

 ganglia, and the very fine auditory nerves pass down on either 



A, 



B 



Fig. 19 



A. ^yt o{ Helix pomtitiat zXl^t C^rrl&cQ.. CiJ.t?, outer corneal layer; C(7.z, inner 

 corneal layer; ep, epithelium of tentacle ; g.op, optic ganglion ; i, lens; 

 Ret, Retina. B. Radular teeth from the odontophore of Helix aspersa, 

 highly magnified. 



side between the closely apposed cerebro-pleural and cerebro- 

 pedal connectives. To see the otocysts, the pedal ganglia 

 should be carefully cleared of connective tissue, and made 

 transparent by mounting in glycerine. 



The snail is hermaphrodite (monoecious) but not self-fertil- 

 ising, and, as is usual in such cases, the generative organs are 

 extremely complex. The essential organ of reproduction, the 

 ovotestis (sometimes called the hermaphrodite gland), is a 

 small yellowish body embedded in the digestive gland in 



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