ON POLYPS. 23 



an Italian author elegantly expresses it, 6C palpare la luce," to feel 

 the light. 



(29.) The tentacles placed around the mouth are eminently sensi- 

 tive, and the smallest particles which impinge upon those organs in 

 their expanded state appear to excite a perception of their presence ; 

 yet their movements, as well as those of the whole body, are extremely 

 slow and languid : it would be difficult therefore to imagine that 

 creatures apparently so helpless should be able to obtain other 

 prey than such as had no power of resistance ; and we could scarcely 

 believe, were it not a matter of continual observation, that the most 

 active little animals, entomostraca, the larvse of insects, and even 

 minute fishes, form their usual food. 



When the hydra is watching for prey, it remains expanded, 

 (fig. 4, 1, 2,5,) its tentacula widely spread and perfectly motionless, 

 waiting patiently till some of the countless beings which populate the 

 stagnant waters it frequents, are brought by accident in contact 

 with them : no sooner does an animal touch one of the filaments 

 than its course is arrested as if by magic ; it appears instantly fixed 

 to the almost invisible threa,d, and in spite of its utmost efforts is 

 unable to escape ; the tentacle then slowly contracts, and others are 

 brought in contact with the struggling prey, which thus seized is 

 gradually dragged towards the orifice of the mouth, that opens to 

 receive it, and slowly forced into the interior of the stomach. 



(30.) We are naturally led to ask, what is the nature of the action 

 by which a passing animal is thus seized ? Trembley supposed that 

 the filamentary arms were besmeared with an adhesive secretion 

 like bird-lime, by which the victim became glued to the tentacle ; 

 this however can hardly be the case, as the exercise of the power of 

 retaining prey seems quite under the control of the hydra : when 

 hungry, seven or eight monoculi* will be captured and swallowed in 

 succession ; but when thus gorged with prey, or when indisposed to 

 take food, although these animals may touch the tentacula again 

 and again, they escape with impunity. 



(31.) Arrived in the stomach of the polyp, the animal which has 

 been swallowed is still distinctly visible through the transparent 

 body of the hydra, which seems like a delicate film spread over it : 

 (Jig* 4, 4,) gradually the outline of the included victim becomes 

 indistinct, and the film which covers it turbid ; the process of diges- 

 tion has begun ; the soft parts are soon dissolved and reduced to a 



* Minute crustaceous animals, possessing considerable strength and agility. 



