HABITS OF HYDRA. 485 



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 Polyp'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. 



1047. When the difference between the external integument 

 and the lining of the stomach is considered, it seems not a little 

 wonderful that the two should be mutually convertible. Yet 

 such is the fact. Amongst the many curious experiments per- 

 formed 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 integument, and from it the buds are produced, which 

 will be presently described ; whilst the tegumentary membrane 

 seems to be capable of speedily doing all that is necessary, towards 

 the digestion of the food. The remarkable power with which 

 these Polypes are endowed of adapting themselves to circum- 



