CHAPTER I. 



OP THE NERVOUS SYSTEM, ITS FORMATION, AND THE VARIOUS 

 SORTS OF FUNCTIONS THAT IT CAN FULFIL. 



The nervous system, in man and the most perfect animals, consists 

 of various quite distinct special organs and even systems of organs, 

 which are closely connected and form a very comphcated whole. It 

 has been supposed that the composition of this system is everywhere 

 the same, except for its greater or lesser development, and the differ- 

 ences of size, form, and situation involved by the various types of 

 organisation. On this theory the various sorts of functions, to which 

 it gives rise in the most perfect animals, were all regarded as being 

 characteristic of it throughout all animal organisation. 



This manner of regarding the nervous system throws no Hght on 

 the nature of the organs in question, on the mode of their origin, on 

 the growing complexity of their parts in proportion to the complication 

 and perfection of animal organisation, nor, lastly, on the new faculties 

 which it confers on animals in proportion to its development. On 

 the contrary, instead of erdightening physiologists on these matters, 

 it leads them to attribute everywhere to the nervous system in various 

 degrees of concentration the faculties which that system confers on 

 the most perfect animals, and this is entirely without foundation. 



I shall therefore endeavour to prove : (1) That this system of organs 

 cannot be a property of all animals ; (2) that at its origin, that is, 

 at its greatest simphcity, it only confers on the animals which possess 

 it the one faculty of muscular movement ; (3) that afterwards, when 

 more highly developed, it endows animals not only with muscular 

 movement but also with f eehng ; (4) that lastly, on reaching completion, 

 it confers on the animals which possess it the faculties of muscular 

 movement, of experiencing sensations, and of forming ideas, com- 

 paring them together, and producing judgments ; in short, of having 

 an intellect whose development is proportional to the perfection of 

 organisation. 



