HYDKfD. 



hollow internally, and communicate with the stomach. They are 

 provided with vibratile cilia, and are furnished with a great number 

 of papillae disposed spirally, and containing in their interior a number 

 of capsules provided each with thread cells. These threads, which 

 are of extreme tenacity, are thrown out when the animal is irritated 



Fig. 41. Hydra viridis (Trembley). i. Hydra magnified, bearing an embryo ready to detach 

 itself. 2. Animal, natural size. 



by contact with any strange body. We may see these filaments 

 wrapping themselves round their prey, sometimes even penetrating 

 its substance, and effectually subduing the enemy. The green 

 Hydra has thus a very simple organisation. Nevertheless, it would 

 be a mistake to say the animal was imperfect, for it possesses every- 

 thing necessary for its nourishment and for the propagation of its 

 species. 



