A STUDY OF LOWER LIFE. 51 



We have already noted that the hydra possesses the 

 power of appreciating sensations, since it shrinks when 

 touched, and exhibits other proofs of its sensitiveness. In 

 the possession of this power, the polype resembles some 

 plants, and most, if not all other animals, including man 

 himself. Broadly stated, this power which the hydra pos- 

 sesses may be regarded as presenting us with the idea of 

 a nervous system in its simplest phase. The functions of 

 such a system may be summarised in the statement that it is 

 adapted for bringing the animal into relation with its sur- 

 roundings. We thus say that the nervous system exercises 

 the function of " Relation ; " whilst, from the fact that the 

 animal performs this function through impressions being made 

 upon it, we are also accustomed to speak of the nervous 

 power as exercising the function of " Irritability." This 

 power, in fact, stands mediately between the animal and the 

 world in which it lives. The higher we ascend in the 

 animal scale, the more perfectly do we find the nervous 

 system adapted for placing the animal in possession of a 

 knowledge of its environments; although, as will be presently 

 remarked, the differences between the nervous powers of 

 higher and lower animals are to be considered rather 

 differences of degree than of kind. 



But as an examination of the hydra demonstrates to us, 

 the view just taken of the nervous functions can hardly be 

 considered of complete kind. For we find that the polype, 

 when touched, is enabled to act upon the "knowledge" 

 or " sensations " which the touch conveys ; since its tentacles 

 contract and its whole body shrinks as if in irritation and 

 alarm. The reception of a sensation by the nervous system 

 is therefore accompanied by a power of acting upon " in- 

 formation received ; " and it cannot be doubted that a 

 certain and definite correspondence must exist between 

 the impression and the act it evokes. Indeed, amongst 

 lower forms of animal life this correspondence is not only 

 exceedingly well marked, but constitutes in itself the sum 

 total of the nervous functions in such beings. But the 



