12 



Lessons in Zoology. 



the mouth, an opening leading into the central hollow 

 or stomach. 



The tentacles are hollow, like so many glove fingers 

 pushing out around the mouth. They are the hydra's fish- 

 ing rods, bearing numbers of little pockets, — the thread- 

 cells — on their sides, in which the fishing lines are coiled up. 

 Each line, instead of a hook at the end of it, has three 

 poisoned darts just where it issues from the pocket. 



^"^iJi' 



Fig. 1. 



Fig 2. 



Fig. 3. 



Fig. 2 represents a portion of a tentacle highly magnified, 

 with the thread-cells in clusters on its surface. Fig. 3 

 is a single cell after it has burst and the thread uncoiled. 

 When a tentacle touches a tiny worm or crustacean, 

 the pockets burst, and the lines entangle the prey in their 

 coils, while the poisoned darts quickly paralyze it. If 

 some creature too large to be paralyzed is caught by the 

 lines, then ensues a grand " tug of war " between that 

 and the h^dra. 



I once watched ancb a atmggle between a hydra and the larva of 

 an ioBect, which lasted an honr and three quarters. Even then the 

 resnlt was donbtinl, bnt nnfortnnately the dish containing the com- 



