72 ZOOLOGICAL PHILOSOPHY 



at the head of the animal kingdom, the general series exhibits a real 

 degradation in organisation ; since after the first four classes all 

 the animals of the following classes are without a skeleton and con- 

 sequently have a less perfect organisation. 



But this is not all : Degradation may be observed even among 

 the vertebrates themselves ; and we shall see finally that it is found 

 also among the invertebrates. Hence this degradation follows from 

 the fixed plan of nature, and is at the same time a result of our follow- 

 ing her order in the inverse direction ; for if we followed her actual 

 order, if, that is to say, we passed along the general series of animals 

 from the most imperfect to the most perfect, instead of a degradation 

 in organisation we should find a grow^ng complexity and we should 

 see animal faculties successively increasing in number and perfection. 

 In order to prove the universal existence of the alleged degradation, let 

 us now rapidly run through the various classes of the animal kingdom» 



MAMMALS. 



Animals with mammae, four jointed limbs, and all the organs essential 

 to the most perfect animals. Hair on certain parts of the body. 



Mammals {Mammalia, Lin.) should obviously be at one extremity 

 of the animal chain, viz. that which contains the most perfect animals 

 and the richest in organisation and faculties ; for among them alone 

 are found those with the most developed intelligence. 



If perfection of faculties is a proof of that of the organs they are 

 based upon as I said above, all mammals (and they alone are truly 

 viviparous) must have the most perfect organisation, since it is agreed 

 that these animals have more intelligence, more faculties and a more 

 perfect set of senses than any others ; moreover their organisation 

 approaches most nearly to that of man. 



Their organisation exhibits a body whose parts are stiffened by a 

 jointed skeleton, which is generally more complete in these animals 

 than in the three other classes of vertebrates. Most of them have four 

 articulated limbs appended to the skeleton ; and all have a dia- 

 phragm between the chest and abdomen ; a heart with two ventricles 

 and two auricles ; red warm blood ; free lungs, enclosed within the 

 chest, through which the blood passes before being driven to the other 

 parts of the body ; lastly, they are the only viviparous animals, for 

 they are the only animals in which the foetus although enclosed within 

 its membranes is always in communication with its mother and develops 

 at the expense of her substance, and in which the young feed for some 

 time after their birth on the milk of her mammae. 



