78 ZOOLOGICAL PHILOSOPHY 



Independently of the degradation of organisation indicated by the 

 shape of the heart, by the temperature of the blood which scarcely 

 arises above the level of the environment, by the incomplete respira- 

 tion and by the almost regular simpHfication of the lung, it is found 

 that reptiles differ considerably among themselves ; so that there ar& 

 greater differences of organisation and external shape among the 

 animals of the various orders of this class than among those of the 

 two preceding classes. Some habitually live in the air, and of these,, 

 such as have no legs can only crawl ; others Uve in the water or on 

 its banks, sometimes withdrawing into the water and sometimes- 

 going into open places. There are some that are clothed in scales 

 and others that have a naked skin. Lastly, although they all have a 

 heart with one ventricle, in some there are two auricles, while in 

 others there is only one. All these differences are due to environment, 

 manner of Ufe, etc. ; conditions which doubtless act more strongly 

 upon an organisation that is still remote from the goal to which nature 

 is tending, than they could do on one more advanced towards per- 

 fection. 



Reptiles are oviparous animals (including even those in which 

 the eggs are hatched in the body of the mother) ; their skeleton is 

 modified and usually very degraded ; their respiration and circulation 

 are less perfect than those of mammals and birds ; and they all 

 have a small brain which does not fill the cavity of the cranium. 

 Hence they are less perfect than the animals of the two preceding 

 classes, and in their turn confirm the fact that the degradation 

 of organisation increases, according as we approach the most 

 imperfect animals. 



Within this class of animals themselves, independently of the modi- 

 fications in their parts due to environment, we find in addition traces 

 of the general degradation of organisation ; for in the last of their 

 orders (the batrachians) the individuals, when they are first born, 

 breathe by gills. 



If the absence of legs observed among snakes were regarded as a 

 result of degradation, the ophidians ought to be the last order of 

 reptiles ; but it would be a mistake to suppose this. The fact is that 

 snakes are animals which for purposes of concealment have adopted 

 the habit of crawhng directly on the groimd, and their body has thus- 

 acquired a considerable length, out of proportion to its size. Now 

 elongated legs would have impeded their efforts in crawhng and 

 conceahng themselves ; while very short legs, of which there could 

 only be four since these animals are vertebrates, would have been 

 incapable of moving their body. Thus the habits of these animals- 

 have caused the disappearance of their legs ; although the batrachians. 



