X.] THE FRESH- WATER POLYPES. 103 



9. Press out an ovary : according to its stage of develop- 

 ment there will be found in it 



a. Simply ectoderm cells with an unusual prepon- 

 derance of the smaller form. 



P. Imbedded among cells like a, one which has 

 become larger and clearer than the rest, and 

 possesses a distinct central clear spot in it. 



7. Considerable aggregation of granular proto- 

 plasm round this cell, so as to form a body 

 consisting of a granular protoplasmic mass, in 

 which is imbedded a clear round vesicle which 

 again contains a distinct rounded dot. 



S. The ripe ovum. Consisting of a great irregu- 

 larly branched mass of protoplasm (vitellus), in 

 which is a clear space (germinal vesicle) con- 

 taining another body (the germinal spot), 



e. The segmented ovum: composed of a large 

 number of small cells. Its thick capsule, 

 rough on its external surface. 



