The Ovogenesis of Hydra. 297 



many eggs in the same ovary. My own observation is not yet 

 sufficiently extensive to state this as an invariable rule; I suggest 

 it to elicit added observations. Ovaries with two or more eggs, 

 each with a separate nucleus, such ovaries as are figured in Fig. 1, 

 Plate 11, are common in H. dioecia, but I have nevei' seen such in 

 other species. Nussbaum states that H. fusca and H. grisea may 

 have two or even more eggs in each ovarj^ I am .inclined to think 

 that the statement is due to a confusion of H. dioecia with the other 

 species, a confusion which will, I believe, account for many of the 

 conflicting statements regarding the habits of hydra. 



In my experiments, largely with H. dioecia, I failed to induce 

 the formation of sex organs by means of cold as R. Hertwig has 

 done with H. fusca. These experiments, he thinks, are therefore 

 •'sehr unvollkommen" and the failure he considers an additional 

 reason for hesitation in ascribing the new specific name, as it de- 

 monstrates, I presume, the general unreliability of my conclusions. 

 But D. D. Whitney found in the case of H. viridis that merely 

 putting the hydras into the cold did not produce the sex organs; 

 they must, after prolonged exposure to the cold, be brought into a 

 higher temperature. Such différences in physiological behavior 

 between H. fusca and H. viridis may well permit the inference that 

 a similar difi:erence would prevail between H. fusca and H. dioecia. 

 My failure to obtain the same results as ß. Heetwig, instead of 

 being an added reason, then, against the specific separation of the 

 two forms, may well be used as an added argument for such sepa- 

 ration. 



I merely wish here, without prolonging the discussion, to justify 

 my former opinion and the present continued use of the new specific 

 name. Additional careful observation can alone decide whether the 

 new species is really such or merely a variety, but the evidence so 

 far adduced seems to favor the former alternative. 



3Iethods. 



No better method of killing has been devised than that before 

 found effective. The animal is placed in a drop of water in a watch 

 glass and allowed to expand fully. Ten c. c. of one half per cent 

 osmic acid is then added quickly; death is instantaneous. The hydra 

 is at once lifted from the acid and put into Merkel's fluid; this 

 has been allowed to act varying times up to several days : six hours 

 is adequate for fixation; twenty four hours is not excessive. 



20* 



