524 BIOLOGY. 



its inferior organs of sense, the antagonism makes its 

 appearance also in the ovarium. A half of the ovaritun 

 is converted into the testis. 



The Snail is therefore a Mollusc, which is female upon 

 one side, male upon the other. 



3215. The androgynous or bisexual animal is, as a 

 general rule, asymmetrical. 



3216. The mantle also or the branchial cavity obeys 

 this want of symmetry. The branchiae of one side dwindle 

 down ; those of the other turn with the mantle towards 

 the head, and the respiratory aperture occurs upon the 

 back. 



3217. With the one-sided evolution of the mantle, 

 one shell also is only developed, while the other is 

 stunted or placed under arrest. The Snail's shell is one 

 of the Bivalve Mollusc's shells, its operculum is the 

 other. This last is stony, horny, and finally is entirely 

 wanting. 



It is remarkable that the right shell has been pretty 

 generally perfected, while the left dwindles down into the 

 operculum ; all the Snail's openings are therefore upon 

 the right side, such as the anus, with the orifices for 

 the escape of the ova and semen. 



Male animals are situated on the right side, female 

 on the left ; or where the right side was predominating, 

 there originated the male sex, where the left, the female. 



3218. As the orifice of the mantle and the shell is 

 properly the aperture of the branchial foramina ; so can 

 it be said, that the Snail were a Mussel, which does not 

 simply extend the foot, but also the mouth or head to 

 the branchial opening ; it is a Mussel reversed. 



3219. Every thing else in the Snails is arranged in 

 accordance with these fundamental organs and forms. 



The cephalic portion of the intestinal canal is indicated 

 also by muscular fibres. The pharynx and the mouth 

 can contract and expand, seize and bite off ; the former 

 frequently admits of being protruded and retracted as a 

 fleshy proboscis with perforating m axilla?,. 



3220. Since the muscular fibres are only tegumental 



