HABITS OF HYDRA. 521 



round its prey. The digestive process never seems to affect 

 them, however, in the slightest degree ; even though they remain 

 thus inclosed during the whole period of the solution of the 

 food. Trembley, the first discoverer of these Hydrde, to whose 

 accurate description of their habits scarcely anything has been 

 added by subsequent observations, once witnessed a very curious 

 circumstance. " Two Polypes had seized upon the same animal ; 

 both had partially succeeded in swallowing it ; when the largest 

 put an end to the dispute, by swallowing its opponent, as well as 

 the subject of contention. Trembley naturally regarded so 

 tragical a termination of the affray as the end of the swallowed 

 Polype's existence ; but he was mistaken ; for, after the devourer 

 and his captive had digested the prey between them, the latter 

 was regurgitated safe and sound, and apparently no worse for the 

 imprisonment." It has been noticed that, when the Hydra is 

 gorged with food, its tentacula may be touched with impunity 

 by the animals, whose contact would at other times arouse it 

 into active movement. This scarcely proves, however, an exer- 

 cise of the will, to which some have referred it. We may easily 

 understand that the distention of the whole of the tissues with 

 fluid may be unfavourable to their contractility; and we have a 

 parallel case in the Human being, for every one can perceive the 

 difference in the facility of swallowing, at the commencement and 

 termination of a full meal. It will scarcely be asserted that this 

 variation is an effect of the will ; in fact, it is often opposed to 

 it, being one of those beautiful adaptations, by which the welfare 

 of the economy is provided for, but which the indulgence of the 

 sensual appetites opposes. 



1170. Amongst the many curious experiments performed on 

 these animals by Trembley, was the following : By means of a 

 fine wire, he actually succeeded in turning the Hydra inside-out, 

 as we might the finger of a glove ; and this violent disturbance 

 did not seem to interfere with the comfort of the animal, for all 

 its functions soon went on as before. What was previously the 

 lining membrane of the stomach now becomes the external in- 

 tegument, and from it the buds are produced, which will be pre- 

 sently described ; whilst the tegumentary membrane seems to be 

 capable of speedily doing all that is necessary, towards the di- 



