Chap, xm.] 



CIRCUIATION. 



197 



In the other veiiebrates there is a heart, but we see it perfecting 



" ^^ ^t .O ^E 



0^1 j 



t T 1 1 ^ 



Fia. 18. 



Schematic figures showing the comparison of the modifications of the circulatory centres 

 in the moliwsfcs : A, pai-t of tho dorsal trunk and of the transversal vessels of a worm ; 

 By heart and auricle of a nautilus ; G, heart and ventricle of a lammelibrandhian or loUgi/nate; 

 J), the same organ in an octopus; E, heart and auricle of a gasteropod; v, ventricle ; o, 

 auricle ; a c, cephalic artery ; a i, abdominal artery. The arrows indicate the direction 

 of the sanguineous current. 



itself little by little. The simplest form of the heart in verte- 



W0 



Fig. 19. ' 



Schema of the framework of 

 the great tru)/ks, of the dif- 

 ferentiated apparatus of the 

 hranchial vessels ; a, arterial 

 .hulb ; 1 — 5, arterial arcs ; 

 a a", aorta ; c,^ carotid artery. 



Heart, branchial arteries, and opercu- 

 lary branchia of the Lepidosteus 

 osaeus; v, ventricle ; A A, auricle; 

 B, arterial muscular bulb ; a, trunk 

 of the branchial arteries ; 1, accessory 

 branchia (operculary) ; p, pseudo- 

 branchia (vent branchia) ; 2, 3, 4, 6, 

 branchiae of the arcs. Tlie arrows 

 indicate the direction of the blood. 



brates exists in fishes. There, the cardiacal dilatation is merely 



