22 HYDROZOA. 



derm unite together, and " the junction between 

 the two is distinctly marked by a clear line." 



The food of the Hydra consists, for the most 

 part, of minute fishes, crustaceans, worms, and 

 such other living creatures as come within the 

 reach of its tentacles ; and it is curious to observe, 

 how, by means of these apparently fragile cords, 

 animals are secured which would be deemed, at 

 first sight, superior to their captor in strength and 

 activity. There can, however, be little doubt, that 

 the tentacles are aided in the performance of 

 their prehensile function by the action of the 

 thread-cells, with which they are so well provided. 

 The elastic filaments of some of these are usually 

 projected into the body of the captured organism, 

 over whose motions they would appear to exert a 

 potent benumbing influence, to the production of 

 which the fluid contained in the interior of the 

 cells probably serves to contribute. For it has 

 even been observed that soft-bodied animals, which 

 succeed in effecting their escape from the grasp of 

 the Hydra, do not, in some instances, recover, 

 but, soon afterwards, die. The entire surface of 

 the tentacles is not at once brought into contact 

 with the body of their victim, and, in the use of 

 these organs, much instinctive caution is shown. 

 When sufficiently mastered, the prey is thrust into 

 the internal cavity, though the act of ingestion 

 does not, in all cases, immediately put an end to 

 its struggles. Grradually, the nutritive matters 

 contained in its body are imbibed by the Hydra, 

 all indigestible portions being finally expelled 

 through the mouth. But some writers describe a 

 short narrow canal, leading from the inner cavity 

 to a small aperture, situate in the centre of the 



