538 THE SENSORIAL FUNCTIONS. 



the largest specimens of the last named tribe, 

 some of which are nearly two feet in diameter. 

 All these animals give but very obscure indica- 

 tions of sensibility; for the contractions they 

 exhibit, when stimulated, appear to be rather 

 the effect of a vital property of irritability than 

 the result of any sensorial faculty. Analogy, 

 however, would lead us to the belief that many 

 of their actions are really prompted by sensa- 

 tions and volitions, though in a degree very 

 inferior to those of animals higher in the scale 

 of being ; but whatever may be their extent, 

 it is probable that the sensorial operations in 

 these animals take place without the inter- 

 vention of any common centre of action. It 

 is at the same time remarkable that their 

 movements are not effected by means of mus- 

 cular fibres, as they are in all other animals ; 

 the granular flesh, of which their whole body 

 is composed, appearing to have a generally 

 diffused irritability, and perhaps also some de- 

 gree of sensibility ; so that each isolated granule 

 may be supposed to be endowed with these com- 

 bined properties, performing, independently of 

 the other granules, the functions both of nerve 

 and muscle. Such a mode of existence exhibits 

 apparently the lowest and most rudimental con- 

 dition of the animal functions. Yet the actions 

 of the Hydra, of which I have given an account, 

 are indicative of distinct volitions ; as are also, in 



