272 AMPHIPNEUSTA. 



as complete as the others." Cuvier further ob- 

 serves that whilst the hranchicB subsist, the aorta, 

 in coming from the heart, is divided into as many 

 branches on each side as there are hranchice. 

 The blood of the hranchicE returns by the veins, 

 which unite towards the back in a single arterial 

 trunk, as in the fishes ; it is from this trunk, or 

 immediately from the veins which form it, that 

 the greatest part of the arteries which nourish 

 the body, and even those which conduct the 

 blood for respiration in the lung, spring. But 



SKELETON OF SIREN. 



in the species which lose their hranchice naturally, 

 the branches which go there become obliterated, 

 except two which unite in a dorsal artery, and of 

 which each gives off a small branch to the lung. 

 " It is," adds this eminent comparative anatomist, 

 " the circulation of a fish metamorphosed into the 

 circulation of a reptile." 



The same author observes that it had been 

 objected that it would be impossible for these 



