AYDRID.-E. IIS 
hollow internally, and communicate with the stomach. They are 
provided with vibratile cilia, and are furnished with a great number 
of papillz: 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 (frembley). 1. 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. 
I 2 
