H4 



THE OCEAN WORLD. 



stagnant ponds, and more especially to the under surface of the 

 leaf. The animal is composed of a small greenish tubular sac, 

 closed at one of its extremities, open at the other, and bearing 

 round this opening from six to ten tentacles, very slender, some- 

 times not exceeding a line in breadth. The tubulous sac is the 



Fig. 40. Hydra vulgaris. i. Hydra with ovum and young, unhatched. 2 Hydra of natural size 

 attached to a piece of floating wood. 3. Egg ready to burst its covering;. 



body of the animal (Fig. 41), the opening is at once its mouth and 

 the entrance to the digestive canal ; the appendages, the tentacula 

 or arms. 



The Hydras have no lungs, no liver, no intestines, no nervous 

 system, no heart. They have no organ of the senses, except those 

 which mav exist in their mouth and skin. The arms or tentacles are 



