252 CIRCULATION IN GASTEROPODA AND CEPHALOPODA. 



is distributed to the gills e; and thence it returns to the heart, 

 after having undergone aeration. Now if a second heart had 

 been placed on the trunk //, just as it is about to subdivide 

 for the distribution of the blood to the gills, the circulation 

 would have been analogous to that of Birds and Mammals. 

 There is a great variety in the position of the gills in Mollus- 

 cous animals, and a corresponding variety in the situation of 

 the heart, which is usually placed near them. In the Doris 

 the gills are arranged in a circular manner, round the termina 

 tion of the intestinal canal ; but in many Mollusca they form 

 straight rows of fringes on the two sides of the body. In 

 these last, the heart not unfrequently has two auricles ; but 

 these are not analogous to the two auricles of Eeptiles ; for 

 each has the same function with the other the reception of 

 the blood from the gills of its own side. 



291. There is a very interesting variety in the conformation 

 of the heart in the CEPHALOPODA, or Cuttle-fish tribe; which 



vb 



.... br 



ab 



\ 



vv av a cs vv 



Fig. 140. CIRCULATING APPARATUS OF CUTTLE-FISH. 



seems to form a connecting link between the plan of the cir- 

 culation that prevails among the Mollusca in general, and that 



