GENERAL CHARACTERS OF VERTEBRATA. 43 



interior of the body of a Cock-chafer, will give an idea of its complexity and 

 variety, and of the large portion of the trunk which is occupied by it ; and 

 will also show the division of the skeleton into segments, the number of which 

 in Insects is limited to thirteen. These are nearly equal and similar to each 

 other in the Larva ; but, in the perfect Insect, the three behind the head are 

 united into the thorax, to which the legs and wings are attached ; and the 

 remainder form the abdomen, which has little concern in locomotion. 



General characters of Vertebrata. 



31. In none of the three preceding divisions of the Animal kingdom, does 

 the Nervous System attain such a degree of development, as to give it that 

 predominance in the whole fabric, which it evidently possesses in VERTE- 

 BRATA. In the Radiata and Mollusca, its functions are obviously restricted^to 

 the maintenance of the nutritive operations ; and to the guidance of the ani- 

 mal, by means of its sensory endowments, in the choice of food, as well as (in 

 some instances) in the search for an individual of the opposite sex : in the 

 Articulata, its purpose appears similar, but is carried into effect in a different 

 manner, the locomotive organs being the parts chiefly supplied by it. In the 

 Vertebrata, on the other hand, the development of all the other organs appears 

 to be subordinate to that of the Nervous System ; their object being solely to 

 give to it the means of the exercise of its powers. This statement is not, of 

 course, as applicable to the lower Vertebrata as it is to the higher ; but it is 

 intended to express the general character of the group. The predominance 

 of the nervous system is manifested, not only in the increased size of its cen- 

 tres, but also in the special provision which we here find, for the protection of 

 these from injury. In the invertebrated classes, wherever t&e nervous system 

 is enclosed in any protective envelope, that envelope serves equally for the 

 protection of the whole body. This is the case, for example, in regard to the 

 spiny integument of the Star-Fish, the shell of the Mollusca, and firm jointed 

 rings of the Insect. The only exceptions occur in a few tribes, in which the 

 nervous system is much concentrated ; and in which the general organization 

 approaches that of the Vertebrata.* In Vertebrated animals, we find that the 

 skeleton essentially consists of a series of parts, which are destined to enclose 

 the nervous centres, and to give attachment on their exterior to the muscles by 

 which the body is moved: hence it may be termed the neuro-skeleton; in 

 contra-distinction to the dermo-skeleton, which envelops the whole body .iff' 

 many Invertebrata, being formed on the basis of their integument. The tis- 

 sues, bone and cartilage, of which the former is composed, are more closely 

 connected with the vascular system, than are the hard parts of Invertebrata ; 

 and are consequently more capable of undergoing interstitial change. 



32. In considering the essential character of the skeleton of Vertebrata, we 

 should look' at its simplest forms, those in which it has the least number of 

 superadded parts. We find these in the Serpent tribe among Reptiles, and 

 in the Eel and its allies among Fish. If we examine their skeletons, we per- 

 ceive that the Spinal Column, with the cranium at its anterior extremity, con- 

 stitutes the essential part of the vertebrated framework ; and that the develop- 

 ment of members is secondary to this. The Spinal Column usually consists 

 of a number of distinct bones, the Vertebrae ; each of which is perforated by 

 a large aperture, in such a manner that, when the whole is united, a continu- 



* Thus, in the highest Crustacea, there is an internal projection from the shell, on 

 each side of the median line, which forms a sort of arch enclosing the ventral cord ; and 

 in the naked Cephalopoda, the nervous centres are supported, and in part protected, by 

 cartilaginous plates, which are evidently the rudiments of the internal skeleton of the 

 Vertebrata. 



