2O8 GEO. W. TANNREUTHER. 



vesicle. The vesicular wall is very thin and the four sperm pass 

 through it when mature and become free within the distal end of 

 the cyst (Fig. 4). The mature sperm are very active within the 

 cyst and finally escape to the exterior through a small temporary 

 opening of the spermary. After the mature sperm have all 

 escaped, the opening closes until more sperm mature. When the 

 spermaries are extremely large, this process continues from forty 

 to fifty hours. 



In order to show the four sperm within a common vesicle, it 

 is necessary to dissect the living spermary apart, as the sperm 

 always escape from the common vesicle before passing to the 

 exterior. The individual cysts when separated become more 

 spherical (Figs, n and 12), and the different stage of develop- 

 ment in the living sperm can easily be distinguished. 



Kleinenberg in his description of the sperm in Hydra viridis 

 definitely states that the sperm are formed from interstitial cells 

 that have divided a number of times; ultimately the nucleus of 

 the cell (the spermatocyte of the first order) disintegrates while 

 the cell substance becomes granular, and in place of the nucleus 

 there appears from one to four refractive bolies, which give rise 

 to the sperm. The refractive bodies referred to beyond doubt 

 result from the two divisions of the nucleus, which he thought 

 disintegrated. The four nuclei (spermatids) within the common 

 vesicle do have the appearance of refractive bodies, especially in 

 'the living material. 



Korotneff (5) gave similar results. He states that the sperm 

 form directly from the nuclei of a multinucleate mother cell. 

 Downing (2) does not mention this interesting phenomenon, 

 which is found in Hydra viridis and Hydra sp. ? (Brauer). 



The mature sperm possess extreme vitality and may remain 

 active from one to three days after escaping from the spermary. 

 The mature sperm of any individual spermary possess about the 

 same degree of fertility. No degenerating spermatogonia were 

 found. 



In the monoecious form Hydra viridis the spermaries become 

 mature before the ovaries. Occasionally sperm and ova on one 

 individual would ripen at the same time, making self-fertilization 

 possible. In order to prove that self-fertilization did occur, indi- 



