638 BIOLOGY. 



since the Ruminant animals in general have many resem- 

 blances in common with Birds, especially in the develop- 

 ment of the horny substance, which obviously agrees 

 with the feathers. 



Thirteenth Class. 

 Aistheseozo a, Opthalmozoa Thricozoa. 



3560. All the senses perfect, five digits; the face 

 covered with skin and flesh, the body with hairs ; 

 mammae present. 



3561. The Thricozoa combine in themselves all the 

 animal classes, and indeed, so far as the development by 

 grades makes no distinction, in equal proportion. 



The differences are in no class therefore so numerous 

 and so strongly pronounced as in this ; and yet one is in 

 more doubt almost concerning the rank of the families 

 than in the former classes. It turns out, therefore, that 

 they are not treated according to sound or solid principles, 

 but that these, after the manner in which Natural History 

 is still prosecuted, are despised. 



Upon viewing superficially the groups of Thricozoa, it 

 is certainly difficult to determine, which are the lowest 

 families, although the uppermost ones are very well 

 known ; so that here matters are the reverse of what 

 they were in Plants. In the case of Birds the empirical 

 inquirer into nature knows neither which are the upper, 

 nor which the lower groups ; while in the Reptiles and 

 Fishes he fares still worse. 



It is pretty generally conceded that the Whales are 

 the lowest in point of rank, because their posterior feet 

 are wanting, and in this they certainly do depart the 

 most from the usual or normal form of the Thricozoa ; 

 yet still it is just these animals which form the proper 

 starting-point for the present class. Even the empirical 

 naturalists here begin to employ physio-philosophical lan- 

 guage, and designate these animals by the title of Pish-like 

 Thricozoa. But, if they repeat the Fishes, then there 

 must be Thricozoa, which stand or rank below them, and 



