LECTURE V. 217 



pulmonary apparatus of lobsters and crabs, 

 that pith-like production that is drawn out 

 of their bodies with their legs when they 

 are torn off. 



Ascending to the newly established class 

 of molusca, I find Mr. Hunter acquainted 

 with all the facts which have warranted 

 later Comparative Anatomists in making 

 this distinction ; so that he might himself 

 have formed the arrangement, had his mind 

 been directed to the subject of classification. 

 Speaking of the situation of the heart in 

 the multiform animals now included in this 

 class, he says, it is very various, and seems 

 chiefly to depend on that of the lungs: also 

 that it is differently situated, even in ani- 

 mals of the same kind, as in the snail and 

 slug. With respect to its structure, he says, 

 in the snail, and in many of the inhabitants 

 of shells, it is composed of an auricle and 

 ventricle, whilst in others it has two auri- 

 cles and one ventricle. He thinks that in 

 the single heart with two auricles, it is 

 formed, as, it is in reptiles, to receive the 

 blood both purified and unpurified, and to 



