104 Cuvierian System of Zoology, 



shall afterwards examine what characters ought immediately 

 to succeed them, and form the first subdivisions. 



In considering the animal kingdom according to the prin- 

 ciples that have been stated, and setting aside the prejudices 

 established by the divisions formerly received, if we regard 

 only the organisation and the nature of animals, without 

 reference to their size, their utility, or the more or less perfect 

 knowledge we have of them, or any other incidental circum- 

 stances, we shall find that there are four principal forms, four 

 general plans, if I may be allowed the expression, accord- 

 ing to which all animals appear to have been modelled ; and all 

 the ulterior divisions, by whatever names they may have been 

 decorated by naturalists, are only slight modifications, founded 

 on the developement or addition of some parts, which do not 

 change, in any respect, the essential parts of the plan. 



In the first of these forms, which is that of man and the 

 animals that resemble him the most, the brain and the prin- 

 cipal trunk of the nervous system are enclosed in a bony enve- 

 lope, which forms the skull and the vertebrae ; to the sides of 

 this vertebral column are attached the ribs and the bones of 

 the members, that form the framework [charpente) of the 

 body. The muscles generally cover the bones, which they 

 move, and the viscera * {les visceres) are enclosed in the head 

 and the trunk of the body. 



Animals of this form we call Vertebrated Animals {Am- 

 mdlia nertebratd). They have all red blood, a muscular heart, 

 and a mouth, with two horizontal jaws ; distinct organs of 

 sight, of hearing, of taste, and smell, are placed in the cavi- 

 ties of the face. Vertebrated animals have never more than 

 four limbs {memhres), ihe sexes are always separated, they 

 have all nearly the same distribution of the medullary masses, 

 and of the principal branches of the nervous system. 



In examining closely all the parts of this great division, 

 we shall find some analogy even in species the most remote 

 from each other, arid we can trace the gradations of the same 

 plan, in a descending series, from man to the lowest genus of 

 fishes. 



In the second form there is no skeleton ; the muscles are 

 only attached to the skin, which forms a soft envelope that is 

 contractile in every direction. In many species the skin pro- 

 duces stony coverings called shells, the position and extent of 

 which are analogous to those of the mucous body. The 

 viscera and the nervous system are included in the general 



* Viscera, in common language, is applied generally to the intestines ; in 

 a scientific acceptation, viscus singular, viscera plural, may denote any 

 internal organ or organs. 



