CCELENTERATA AND PORIFERA 



169 



FIG. 195. Photograph of living hydras. Each of the 

 two at the right bears a bud. Twice natural size. 



form much of 



their food. No 



vascular, respira- 



tory, or excretory 



systems are pres- 



ent, and the ner- 



vous system is rep- 



resented only by 



a few scattered 



cells. Delicate 



muscle fibers indicate the beginning of a muscular sys- 



tem in the animal 

 kingdom. 



Reproduction oc- 

 curs in two ways 

 by budding and 

 means of eggs. 

 a Hydra be 

 watched a few min- 

 utes each day for a 

 week, a minute bud 

 which is really an 

 outpushing of the 

 wall may be seen 

 to appear and grow 

 larger from day to 

 day for a period of 

 from four to eight 

 days until it as- 

 sumes the form of 

 the mother. It then 



by 

 If 



?IG. 196. Photograph of Hydra enlarged fifteen 

 diameters. The minute swellings on the ten- 

 tacles at the left are the stinging cells. 



