334 Natural History of British Zoophytes. 



tion of the zoophyte is evidently sedentary ; but the contractions and 

 mutations of the body itself are suflficiently vivacious, while in seiz- 

 ing and mastering its prey it is surprisingly nimble ; seizing a worm, 

 to use the comparison of Baker, " with as much eagerness as a cat 

 catches a mouse." It is dull and does not expand freely in the dark, 

 but enjoys light, and hence undoubtedly the reason why we general- 

 ly find the Hydra near the surface and in shallow water. 



The Hydrae are very voracious, feeding only on living animals,* but 

 when necessary they can sustain a fast of many weeks without other 

 loss than what a paler colour may indicate. Small larvae, worms, 

 and entomostracous insects seem to be the favourite food, and to en- 

 trap these they expand the tentacula to the utmost and spread them 

 in every direction, moving them gently in the water to increase their 

 chances, and when a worm, &c. touches any part of them it is im- 

 mediately seized, carried to the mouth by these flexible and contrac- 

 tile organs, and forced into the stomach. " 'Tis a fine entertainment," 

 says Baker, " to behold the dexterity of a polype in the mastering 

 its prey, and observe with what art it evades and overcomes the su- 

 perior strength or agility thereof. Many times, by way of experi- 

 ment, I have put a large worm to the very extremity of a single arm, 

 which has instantly fastened on it with its little invisible claspers. 

 Then it has afforded me inexpressible pleasure, to see the polype 

 poising and balancing the worm, with no less seeming caution and 

 judgment than a skilful angler shows when he perceives a heavy 

 fish at the end of a single hair-line, and fears it should break away. 

 Contracting the arm that holds it, by very slow degrees, he brings 

 it within the reach of his other arms, which eagerly clasping round 



this they effect in the following manner. When the flat surface of the foot is 

 exposed for a short time to the air, above the surface of the water, it becomes 

 dry, and in this state exerts a repulsive action on the liquid, so that when drag- 

 ged below the level of the surface, by the weight of the body, it still remains 

 uncovered, and occupies the bottom of a cup-shaped hollow in the fluid, thereby 

 receiving a degree of buoyancy, sufficient to suspend it at the siu'face. The 

 principle is the same as that by which a dry needle is supported on water, in the 

 boat -like hollow which is formed by the cohesive force of the liquid, if care be 

 taken to lay the needle down very gently on the surface. If, while the Hydra is 

 floating in this manner, suspended by the extremity of the foot, a drop of water 

 be made to faU upon that part, so as to wet it, this hydrostatic power wiU be 

 destroyed, and the animal will immediately sink to the bottom." — Roget, Bridgw. 

 Tr. i. 179. This passage is nearly a literal translation from Trembley's Hist, 

 des Polypes, p. 37-8- 



* In confinement, however, Trembley found that they might be fed on min- 

 ced fish, beef, mutton, or veal — Mem. 104. 



