50 HYDR^, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 



True eggs are also produced by the hydra. The ovary 

 containing the ova is situated in the body walls near the 

 posterior end of the body. The sperm cells are produced in 

 the walls just below the tentacles. When mature, the 

 ovum is fertilized by the sperm, settles to the bottom, and 

 after lying dormant awhile develops into an adult. 



Regeneration of lost parts. — Many animals are similar to 

 plants in their ability to reproduce lost organs and parts. 

 If a hydra is cut in two near the middle, each part will re- 

 produce the lost part, thus producing two hydrse where 

 formerly there was one. If a hydra is cut into several pieces, 

 each piece, under favorable conditions, will produce a new 

 hydra. Where conditions are favorable to life, a hydra 

 can hardly be killed by mutilation. Hydrse may be cut 

 into pieces and the pieces may be grafted together in all 

 sorts of ways and yet thrive and grow vigorously, as 

 related by Professor Morgan in his interesting book on 

 " Regeneration." 



The Campanularian Htdhoid 

 Class I. — Hydrozoa (water animals) 



The branch Ccelenterata is divided into several classes, 

 representatives of which will be briefly discussed and com- 

 pared with the hydra. 



The hydrozoans are Ccelenterata living in water, either 

 fresh or salt. Some of them are simple in structure, like 

 the hydra, and some of them are very complex, both in 

 structure and development. 



Campanularian hydroid. — This is an exceedingly delicate 

 and beautiful organism found growing in the sea attached 

 to seaweeds, rocks, sunken timbers, etc. It is known as a 



