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 f f 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 Beptiles; 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 cs vc as b 
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 
