FEESH-WATEE POLYP 89 



number constant ? In which layer and from which 

 cells do the testes develop ? Compare the ovaries with 

 the testes. Can you find the ovum itself? Press the 

 cover-glass so as to crush the testes, and note the 

 spermatozoa. "What is their shape ? Size ? Are they 

 motile or motionless? 



Draw a specimen in which these organs are visible. 



An excellent method of preparing isolated cells of the 

 ectoderm and entoderm for study is to put a hydra into 

 MiiUer's fluid for a day, then with fine dissecting nee- 

 dles carefully tease it to pieces in fifty per cent, glyce- 

 rine, and examine under high power. Prepared sections 

 of the body may be made according to the directions 

 given in the revised edition of Huxley and Martin's 

 " Practical Biology." 



