CRISTATELLA. 93 



All these are evidently endowed with their peculiar individual sensa- 

 tion and action ; all originate, live, and die as separate beings. But there 

 is no evidence to indicate that they are animated by a common will, or 

 act in concert. Perhaps this would require a share of intelligence far 

 surpassing what has been assigned to these creatures. Nothing shews 

 that each is affected beyond the external cause affecting itself, or that 

 it performs more than its own peculiar functions. But I have often ob- 

 served, that external causes seem to operate on a whole colony with a 

 similar effect ; thus, while the functions of each are restricted according 

 to its individual sensation, the operation of all may contribute to the com- 

 mon welfare, or to actuate the common basis sustaining the whole. This 

 is not inconsistent with assuming the peculiarities of individual existence. 



Yet it is undoubted that a principle of volition does reside in the 

 mass, and that it does influence its motion. The two portions constitut- 

 ing the specimen, Plate XXVII. fig. 2, when it was artificially sundered, 

 receded from each other as if by common consent. In twenty hours they 

 were nearly an inch apart, and much farther on the following day. But 

 in a week they had come reciprocally nearer together. The hydra? close 

 to the line of division having displayed themselves immediately after the 

 section, prohibits our presuming that such extraordinary violence had 

 severely affected them. 



Two entire specimens, of about equal size, were seated exactly parallel 

 to each other on a vertical branch. By the descent of one of them, they 

 had separated half an inch in forty-eight hours. 



Their motion is inconceivably slow, and their adhesion is usually very 

 slight. 



No other mode of progression than crawling belongs to the Crista- 

 tella. The originating animal is buoyant ; but the adult cannot swim. 

 It is a solid, consistent mass, of considerable specific gravity. 



Motion must therefore result most probably from successive rugosi- 

 ties or inequalities formed on the sole. 



The hydrse are displayed more luxuriantly at night and during genial 

 temperature. Then, their action is most vehement, and the progression of 



