OBSERVATIONS ON THE GERM CELLS OF HYDRA. 



GEO. W. TANNREUTHER. 



The germ cells of hydra, which pass through stages comparable 

 to those of higher animals, possess some peculiarities that have 

 not been previously mentioned. Some investigators advocate the 

 specificity of the germ cells, while others claim that the sex cells 

 are the immediate derivatives of the ordinary interstitial cells. 



Kleinenberg (4), Hertwig (3), Brauer (i) and others consider 

 the sex cells as interstitial in origin and state that the egg first 

 becomes recognizable after the ovary has begun to develop. 

 Downing (2) claims that there is continuity of germ plasm in the 

 sense of a specific line of germ cells, that the egg (Hydra fusca} 

 is always present even before the interstitial cells begin to form 

 the ovary and that the egg may grow rapidly and take the initia- 

 tive in its formation. He furthermore believes that the egg is 

 recognizable as such in the adult hydra and in general that in 

 some stage in the embryonic development certain cells are stamped 

 with sex characters, so that they and their progeny form the sex 

 cells distinct throughout the life of the individual. 



A careful examination of sections from Hydra sp.? (Brauer) 

 gives pretty conclusive evidence that not only the egg but the 

 sperm as well is interstitial in origin. There can be no question 

 in case of the sperm, as the different stages in development can 

 readily be traced from the interstitial cells to the mature sperm. 

 Furthermore, the progenitors of the spermatozoa have no special 

 characters by which they can be recognized as germ cells. The 

 cells that give rise to the eggs are interstitial in position and can 

 be distinguished in the adult hydra from the ordinary interstitial 

 cells by their large nucleus, nucleolus and abundance of chroma- 

 tin, even before the growth of the ovary begins, as Downing 

 states. This is especially true during the breeding season. If 

 these sex cells could be distinguished during the budding season 

 as well, it would at least suggest specificity of the germ cells. 



In the dioecious form Hydra sp. ? (Brauer) the egg cells can- 



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