336 THE BIOLOGY OF HYDRA : 1961 



medusa formation, probably by a feedback action by inducing 

 partial anaerobiosis in the culture water. This problem is related to 

 the sexual differentiation of H. littoralis which also appears on stag- 

 nation, for in both animals the partial anaerobiosis of stagnation in- 

 duces a second pattern of differentiation to be expressed, much as 

 the butterfly pattern in the caterpillar becomes expressed during 

 metamorphosis. 



LYTLE: We have done a similar experiment with the scyphisto- 

 mae of Amelia, although our experiments took a lot longer than 

 yours. We placed scyphistomae in a 5" cold room and left them 

 there for about six months with only an occasional feeding. Shortly 

 after we brought them back up into the laboratory (at 18.5 ), 

 they strobilized. This was the only time we have obtained strobilae 

 in the laboratory, although admittedly we haven't tried too serious- 

 ly. We did try different rates of feeding without any success, but 

 when we left them in the cold room they got dirty and eventually 

 strobilized. 



CROWELL: Something similar happened with specimens of 

 Aurelia which we gave to students at Bellarmine College. They 

 tried, without success, to induce strobilization. Then, by accident, 

 one of the students who had quit working but had a few polyps 

 stored in a refrigerator, got medusae. So we have three explanations. 

 Starvation is important, cold is important, and neglect is important. 



LOOM IS: Calculated neglect. 



CROWELL: Not even calculated neglect. 



