210 



ZOOLOGY. 



move is the especial character of animal life, and these two 

 functions belong to the nervous system. It might readily, 

 then, be anticipated that the mode of conformation of this 

 system would exert a powerful influence over the nature of 

 animals, and would furnish characters of primary importance 

 in classification. 



The general disposition or mode of reunion of the different 

 parts of the body exercises an equally important influence, as 

 modifying the localization of the functions and the division 

 of the physiological result. 



Although it is easy lor the zoologist to distinguish the 

 four groups just mentioned, and to refer to one or the other 

 of them an animal under examination, yet there are some 

 beings which seem connected with two different types, like 

 border lands whose rights of possession have not yet been 

 determined. 



It sometimes also happens that it is difficult to define rigo- 

 rously these four groups; but, to give an exact idea, it will 

 be sufficient to indicate the more prominent characters pecu- 

 liar to each type, and to remark, 

 that the reunion of all these cha- 

 racters is not always to be met 

 with, sometimes one and sometimes 

 another being effaced as we descend 

 to the limits of the division. 



374. The vertebrate animals 

 resemble man in the more impor- 

 tant points of their structure; 

 almost all the parts of their bodies 

 are in pairs, and disposed symme- 

 trically on the two sides of a median 

 longitudinakplane ; their nervous 

 system is highly developed, and is 

 composed of nerves and ganglions, 

 and of a brain and spinal marrow. 

 To these we may add, that the 

 principal muscles are attached to 

 an internal skeleton (Fig. 161), 

 composed of separate pieces, con- 

 nected together, and disposed so as to protect the more impor-. 

 tant organs, and to form the passive instruments of locomotion ; 

 that the more important part of this skeleton forms a sheath for 

 the brain and spinal marrow, and results from the reunion of 



Fig. 162. Nervous System 

 of an Insect (Carabus, a 

 Beetle). 



