16 



TNTUODUCTIOX TO ZOOLOGY. 



terminal sucker is exposed to the air until perfectly dry, in 

 which state it repels the water, and thus becomes an instru- 

 ment for sustaining the body of the little animal in a perpen- 

 dicular position. In this attitude, the tail being at the surface 

 of the water, the head underneath, it stretches out its ten- 

 tacula, like so many fishing-lines, for the capture of its prey. 



These tentacula, there is reason 

 to believe, possess the power of 

 communicating some electric 

 shock, or otherwise stunning the 

 minute inhabitants of the water 

 with which they come in contact 

 {Fig. 8). 



The most common mode of re- 

 production in the Hydra is that 

 by gemmation or buds. Little 

 tubercles are observed to arise 

 on the surface of the animal, 

 which ere long assimie the ap- 

 pearance of the parent, and then 

 separate; but not unfrequently, 

 even while attached to the body 

 of the parent, the young Hydras 

 throw out buds themselves. In 

 this way, three or four young 

 may be seen at the same time depending from the sides of 

 the mother, and in different stages of growth — 



"Where some are in the bud, 

 Some green, and rip'ning some, while others fall." 



For our principal knowledge of the habits of the Hydra we are 

 indebted to Trembley, of Geneva, a naturalist who lived in the 

 last century, and devoted much time and attention to the study 

 of this class of animals. His discoveries were published in 

 1744; and some of the facts he elicited were so astounding 

 that, at first, naturalists refused to give credit to them. He 

 found, for instance, that if a Hydra were divided into two 

 parts, each division became a perfect Hydra, and that the 

 same thing occurred if the creature were cut into forty pieces. 

 Further, he found that if one Hydra were taken, and, by 

 careful management, pulled into the inside of anotlier, the two 

 became incorporated, or formed one body; and that the only 



Fig. 8.— Hydra, 



