The Ovogenesis of Hydra. 299 



mature in spring-, lias been found by D. D. Whitney to form sex 

 organs when taken from a low to a considerably higher temperature; 

 while H. fusca which customarily matures in the fall, has been found 

 by R. Heetwig to develop spermaries when removed from room 

 temperature to lower temperature. 



One would expect that in such closely related forms the real 

 cause of the formation of the sex organs would be identical and 

 that the temperature changes are probably occasions rather than 

 causes of their appearance. R. Hertwig holds this opinion and 

 proposes the hypothesis that the sexual process follows as an effect 

 of the depression of the cells, a depression similar to that of the 

 protozoan before conjugation and which is marked by a disproportio- 

 nately large nucleus. He supports his hypothesis by the following 

 evidence. He has observed that the sexual process frequently follows 

 a prolonged period of budding and that animals that have budded 

 for a long time show degenerative fusion of adjacent cells and 

 enlarged nuclei. Furthermore several observers have recorded the 

 fact that the sexual process in hydra is accompanied by a high rate 

 of mortality, which fact is interpreted to mean that both death and 

 the sexual condition are induced by a common cause — a depression 

 of the organism, a condition said to be marked in the protozoa, by 

 a relatively large nucleus. 



H the presence of relatively large nuclei be an index of de- 

 pression, then the condition should be readily demonstrated by 

 measurement. I have made a series of measurements on several 

 hundred cells of H. dioecia and //. fusca, details of which will appear 

 later when the work is completed, to test this point. Sections were 

 made from two lots of hydras (A), those reproducing sexually and (B), 

 those not so reproducing. Hydra contracts so unsymmetrically, on 

 fixation, that cells on opposite sides of the body are variously shaped, 

 some long and narrow, others contracted and so broad in proportion 

 to the length. As an index of the nucleo-plasma relation, I have 

 divided the diameter of the nucleus by the product of the length 

 and breadth of the cell. This index is, in series A, always less so 

 far as my measurements now go, than in series B: the nucleus is, 

 therefore, relatively small in the sexually mature animals, a result 

 directly contrary to the hypothesis. 



On the other hand, a series of experiments, which may be briefly 

 reported here, were made to see the effect of the presence of the 

 sex organs on the regeneration in hydra: these show that when 



