o38 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 intervention of 

 any common sensorium, or 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 ani- 

 mals, 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 



