IDEAS 



ON THE ORGANIZATION OF ANIMALS BELONGING 



TO THE DIFFERENT CLASSES OF 



THE ANIMAL KINGDOM. 



DIVISION FIBST. 



VERTEBRATE ANIMALS. 



383. The vertebrate animals,* so named by reason of 

 the presence of a vertebral column forming the essential part 

 of the skeleton, are of all animals the most perfect ; and, as 

 was to be expected, those also ( 346) in whom the organs 

 are the most numerous and the most complex. 



They possess an internal skeleton, by which means (?) 

 they attain a size never reached by the articulata, mollusca, 

 and zoophytes; and to this skeleton may be ascribed, no 

 doubt, in part at least, the vigour and precision of their 

 movements. 



This internal skeleton, to which there is nothing analogous 

 in the other great sections of the animal kingdom, is generally 

 composed of bones, and is arranged nearly as in man ; never- 

 theless, as in the skate, the skeleton remains cartilaginous, 

 and there are fishes in which it is all but membranous. We 

 have already studied the skeleton carefully ( 259 to 282). 

 The part which is never absent is the vertebral column and 

 cranium ; other parts may be, and often are, deficient : the ribs 

 are wanting in frogs ; the sternum in serpents, &c. But it 

 is especially in the limbs that varieties of formation are 

 observable; these are sometimes wholly absent, as in the 

 coluber or common snake ; sometimes they are merely dimi- 



* In this sketch of the general type of the vertel>rata, we have taken no 

 account of the amphioxut, whose organization is extremely low in the scale; 

 for in this eccentric being (which in its character approaches fishes), most 

 of the characters peculiar to this great section or division of the animal king- 

 dom are wanting. 



