RESPIRATOnY CIRCULATION IN FISHES. 195 



the requisite power is supplied by two additional hearts, 

 situated on the venae cavae, of which they appear as if they 

 were dilatations, immediately before the branchial arteries 

 are sent ofT."^ They are shown at e, e, Fig. 355, which re- 



presents this part of the vascular system of the Loligo, de- 

 tached from the surrounding parts; the course of the blood 

 being indicated by arrows, c is one of the three trunks 

 constituting the venae cavae, proceeding from above, dividing 

 into two branches as it descends, and terminating, conjointly 

 with the two venous trunks (d,) which are cominir from be- 

 low, into the lateral or branchial hearts (e, e,) already men- 

 tioned. Thence the blood is conveyed by the branchial 

 arteries, (f, f,) on each side, to the gills (g,) and returned, 

 by the branchial veins (i,) to the large central, or systemic 

 heart (l,) which again distributes it, by means of the sys- 

 temic arteries, to every part of the body. The cuttle-fish 

 tribe is the only one thus furnished with three distinct 

 hearts for carrying on a double circulation: none of these 

 hearts are furnished with auricles. 



The remarkable distribution of the muscular powers 

 which give an impulse to the circulating fluids, met with in 



* These veins arc surrounded by a great number of blintl pouches, wliich 

 have the appearance of a fringe; the use of this singular structure is un- 

 known. 



