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THE POPULAR SCIENCE MONTHLY. 



which the Indian skillfully throws over the horse's head as he chases it 

 over the prairies. So the hydra throws out his long, rope-like fingers, 

 and lassoes the little animals that swim near it. Sometimes it gets hold 

 of animals so strong that they may tear the fingers or tentacles, and 

 get away again. But the hydra will not be outdone in this way. He 

 has another weapon at hand. Some of the cells in the outer skin are 

 oval, or egg-shaped, and if you look through the cell-walls you see 

 inside what appears to be a long, coiled thread, with two hooks at the 

 bottom (Figs. 38 and 39). These egg-shaped cells are called "thread- 

 cells" and the hydra ha,s many thousands of them in his feelers or 

 tentacles. This thread or spring darts out of its shell whenever the 

 hydra needs it, and sticks itself into the body of the prey like a sharp 

 harpoon (Figs. 40 and 41). 



Fig. 40 Thread-Cell, with its 

 Thread uncoiled. 



Fig. 41. Thread-Cell, with the Spring 

 turned out like a harpoon. 



If you examine this harpoon closely, you will find that it is only 

 a part of the cell poked in like the finger of a glove turned inward ; 

 and when the fingers, or tentacles, seize an animal, these glove-finger 

 cells that cover the tentacles all dart out. Some of them seem to con- 

 tain a poisonous juice which stupefies or kills the prey in an instant. 

 There is an animal in the sea called the Portuguese man-of-war, 

 which is really a dangerous creature, it has so many of these sharp 

 harpoons. When the prey is stunned or dead, the fingers carry it 

 to the mouth, and it passes down into the long tube or body of the 

 hydra, where it is digested, as though it were in a regular stomach. 

 Along the outside of this funnel-shaped body you may often see little 

 buds, which grow and give off other buds, till the old hydra looks like 



