56 MAMMALIAN DESCENT. [Lect. IT. 



After writing the above, I received from Professor Simon H. Gage, 

 B.S., of Cornell University, Ithaca, N.Y., a most important com- 

 munication on the respiration of certain fresh-water Tortoises. The 

 information thus given covers just a page and a half, and yet it is of 

 more value to the biologist than some biilky volumes that one 

 could name. I shall insert it, bodily. Let the facts there disclosed 

 be but fairly considered, and the difficulty of supposing a gradual 

 melting down of the distinctions between the Amphibia and EeptiHa 

 ■will be at an end. 



The lining of the pharynx, or upper part of the gidlet, is the 

 proper normal respiratory organ of any creature possessed of a 

 notocJiord, or primary spinal axis. All the various siaeoialisations 

 that may be found in Ascidians (Sea-squids), AmpMoxus (the 

 Lancelet), and in all the Vertebrata, are of secondary importance to 

 the enibryologist. The peculiar structure and functions of the 

 pharynx described by Professor Gage may be due to degradation 

 or relapse, but if so, it only proves that the aquatic was once 

 the mode of respiration in the stock from which these Tortoises 

 sprang. 



" Pharyngeal Respiration in the Soft-Shelled Turtle (Aqndonectes 

 spAnifer). By Simon H. Gage of Ithaca, N.Y. 



"During the last twenty-five years the mechanism of respiration 

 in the Chelonia has been investigated with considerable thoroughness, 

 both in this country and in Europe ; and at present the Chelonian 

 form of respiration is considered to be comparable with that of the 

 mammal rather than with that of the frog, as formerly supposed. 

 "While, however, the mechanism of respiration has been quite fuUy 

 investigated, there has been, so far as I am aware, but one who 

 has considered the organs of respiration in the different groups of 

 turtles. 



" Professor Agassiz, in Part II. of the Contributions to Nortli 



■American Zoology (p. 284), states that the lung capacity of the 



soft-shelled turtle is far less in proportion to its body-weight than 



is that of the land turtles. He also states, in considering this fact, 



that the skin on the ventral side of the body, from its rich network 



