GENERAL CHARACTERS OF VERTEBRATA. 53 



to suspect in the lower tribes of animals. These are even much more strik- 

 ing in Man, than in the lower Vertebrata; indeed the comparative slightness 

 of the influence of the mind upon the body, is one of the causes which ren- 

 der the lower Mammalia more able than Man is to recover from the effects 

 of severe injuries. The Mollusca seem to grow like plants ; their massive 

 organs increasing by their own separate vitality, and being but little depend- 

 ent upon each other. Even the act of respiration, which is in most animals 

 performed by a series of distinct muscular contractions, is there principally 

 effected through the medium of the cilia which clothe the respiratory surface. 

 But in the Vertebrata, the nervous system possesses a distinct and independ- 

 ent rank ; its offices are those which more particularly constitute the active 

 life of the animal ; the organic functions have for their chief object, the main- 

 tenance of the nervous and muscular apparatus in the condition requisite for 

 their activity ; and in consequence, all these different kinds of apparatus are 

 so interwoven together, that their mutual dependence is very close. 



24. The foregoing remarks will be found to have an important bearing on 

 the details subsequently to be given respecting the functions of the Nervous 

 system in Man ; and it is desirable to set out with clear ideas on this subject, 

 since there is no department of Physiology, regarding which more error is 

 prevalent. There is no valid reason for believing that the Organic functions 

 in Animals, any more than the corresponding changes in Plants, are depend- 

 ent on the nervous system for their performance ; but common observation 

 shows, that they are much influenced by it in the higher animals ; and from 

 such a comparison as that which has been just now briefly made, it would 

 appear that, the higher the general development of the nervous system, the 

 closer is their relation with it. 



25. This general character of the Vertebrata harmonises well with what 

 may be observed, on a cursory glance at the structure of their bodies, as to 

 the proportion between the organs of Nutritive and those of Animal life. The 

 former, contained in the cavities of the trunk, are highly developed ; but, as in 

 the Mollusca, they are for the most part unsymmetrically disposed. Of the 

 latter, the nervous system and organs of the senses occupy the head; whilst 

 the muscles of locomotion are principally connected with the extremities: 

 both are symmetrical, as in the Articulata ; but, whilst that part of the nerv- 

 ous centres, which is the instrument of reason, is very largely developed, the 

 portion which is specially destined to locomotion, together with the muscular 

 system itself, bears much the same proportion to the whole bulk of the body, 

 as it does in the Articulated series. Hence we observe that the Vertebrata 

 unite the unsymmetrical apparatus of nutrition, characteristic of the Mollusca, 

 with the symmetrical system of nerves and muscles of locomotion, which is 

 the prominent characteristic of the Articulata ; both, however, being rendered 

 subordinate to the great purpose to be attained in their fabric, the develop- 

 ment of an organ, through which intelligence peculiarly manifests itself. For 

 the operations of this, a degree of general perfection is required, which is 

 not met with elsewhere. The higher Vertebrata have a power of constantly 

 keeping the temperature of the body up to a point, which it can only attain 

 occasionally, and under peculiar circumstances, in the Articulata, and which 

 it never reaches in the Mollusca. This involves an energetic performance of 

 the functions of respiration and circulation ; and these again require consider- 

 able activity of digestion. All the Vertebrata have red blood, which is pro- 

 pelled through the system by a distinct muscular heart ; and the number of 

 red corpuscles, which any given amount of the fluid contains, bears a nearly 

 constant proportion to the ordinary temperature of the animal. They are 

 further distinguished from Articulata by a character which seems of little im- 

 portance, but which is very constant in each group. Whilst the mouth of the 



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