DEGRADATION OF ORGANISATION 77 



thus approximate in some ways to the monotremes and cetaceans. 

 We shall then recognise that the palmipeds, waders, and galUnaceans 

 should constitute the first three orders of birds, and that the doves, 

 passerines, birds of prey and chmbers should form the last four orders 

 of the class. Now, from what we know of the habits of the birds 

 of these last four orders, we find that their young on coming out of 

 the egg can neither walk nor feed by themselves. 



On this principle the climbers are the last order of birds ; more- 

 over, they are the only ones which have two posterior digits and two 

 anterior. This character, which they possess in common with the 

 chameleon, appears to justify us in placing them near the reptiles. 



REPTILES. 



Animals with only one ventricle in the heart and still possessing a pul- 

 monary respiration though incomplete. Their skin is smooth or 

 provided with scales. 



In the third rank are naturally and necessarily placed the reptiles ; 

 and they will furnish us with new and stronger proofs of the degrada- 

 tion of organisation from one extremity of the animal chain to the 

 other, starting from the most perfect animals. In fact, their heart, 

 which has only one ventricle, no longer displays that conformation 

 which belongs essentially to animals of the first and second ranks, 

 and their blood is cold, almost like that of the animals of the posterior 

 ranks. 



We find another proof of the degradation of the organisation of reptiles 

 in their respiration. In the first place they are the last animals to 

 breathe by true lungs ; for after them we find no respiratory organ 

 of this nature in any of the succeeding classes, as I shall endeavour 

 to show when speaking of molluscs. Next, the lung has in their case 

 usually very large chambers, proportionally less numerous, and is 

 already much simplified. In many species this organ is absent in 

 youth and is then replaced by gills, a respiratory organ which is never 

 found in animals of the anterior ranks. Sometimes the two kinds 

 of respiratory organs are present together in the same individual. 



But the strongest proof of degradation in the respiration of reptiles 

 is that only part of their blood passes through the lungs, while the rest 

 reaches the parts of the body without having undergone the influence 

 of respiration. 



Finally, among reptiles the four limbs essential to the most perfect 

 animals begin to be lost, and indeed many of them (nearly all the 

 snakes) lack them altogether. 



