50 HYDKvIi, JELLYFlbliKS, HEA Ax\EMU>.E!^, CLiKAL P(.)LVPS 



True eggs are also produced by the hydra. Tlie ovary 

 containing the ova is situated in tlie body walls near the 

 posterior end of the l:)ody. 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 hydi-a; where 

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

 each piece, under favorable conditions, will pi-oduce a new 

 hydra. Where conditions are favorable to life, a hydra 

 can hardly lie 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 

 i-elated by Professor Morgan in his interesting book on 

 " Regeneration." 



The Campanularlvn TIydkoid 

 CInss I. — Iludrozoa (tenter animah) 



The branch Ccelenterata is divided into several classes, 

 representatives of which will be brietij' discussed and com- 

 pared with the hydra. 



The hydrozoans are Ca-lenterata living in water, either 

 fresh or salt. Some of them are simi.ile in strutdure, like 

 the hydra, and some of them are very comjile.x, both in 

 structure and flevelopment. 



Campanularian hydroid. — This is an exceedinglv delicate 

 and beautiful organism found growing in the sea attached 

 t(i seaweeils, rocks, sunken timbers, etc. It is known as a 



