HYDRA. 135 



also made of the tentacula as organs of prehension for seizing 

 and detaining their living prey, and for conveying it to the 

 mouth, where it is quickly swallowed. On the other hand, 

 vs^hen alarmed, or exposed to irritation, the hydra suddenly 

 shrinks, by the gradual contraction of all the tentacula, and 

 of the body also, into a small globule, which might easily 

 escape notice, unless its previous situation were accurately 

 observed. 



It might be asked by what power is this animal, occupying 

 so low a place in the scale of organization, enabled to per- 

 form these actions? To this question, however, no satisfac- 

 tory answer has yet been given. The substance of the hy- 

 dra, when examined by the microscope, appears to be nearly 

 homogeneous, except that a number of grains are intermixed 

 with the pulpy and gelatinous matter composing the princi- 

 pal bulk of the body. These grains, when pressed out of 

 the flesh into water, are scattered indiscriminately; and ap- 

 pear to have been united in the living animal, by means of 

 this glutinous material. 



No perceptible fibres, either muscular, or of any other 

 kind, can be detected in the flesh of the polypus: nor is 

 there the least indication of the formation of transverse 

 rings, similar to those which exist in worms, and which, in 

 these latter animals, contribute to progressive motion. Every 

 portion of the substance of the body is equally irritable and 

 contractile, and its movements appear to be governed by 

 some voluntary power belonging to the animal, and direct- 

 ed to the attainment of certain ends. The softness and pli- 

 ancy which it possesses allow of its being closely fitted to 

 all the inequalities of the surface of the bodies to which it 

 is applied; and perhaps this cause alone occasions it to ad- 

 here with great force to these bodies, without the aid of any 

 glutinous fluid. A conjecture, which has much appearance 

 of probability, has been ofi'ered, that this power of adhesion 

 is derived from the presence of a great numi)cr of exceed- 

 ingly minute disks, interlj^ersed over every part of the sur- 

 face, constituting so many suckers, and resembling, though 

 on a very diminutive scale, the sucking apparatus on the 

 arms of the cuttle-fish. 



