CHARLES F. LYTLE 335 



slowed down. In the interim there is a maximinn in tlie production 

 of frustules. 



It appears that whenever metaboHc reserves are not being 

 siphoned off by hydranth or medusa budding, they become avail- 

 able for the production of frustules. Possibly the reason for the de- 

 cline in frustule production two or three weeks prior to the appear- 

 ance of medusa buds is that some of the reserve materials are al- 

 ready going into the pathway leading to the production of medusa 

 buds before the actual morphological appearance of buds. In 

 other words, the biochemical machinery is being set in motion. Sim- 

 ilar phenomena have been demonstrated in several other develop- 

 mental systems where biochemical differentiation precedes morpho- 

 logical differentiation. 



HAND: That's fine. But as I visualized what you were thinking 

 about, it seemed to me that you were saying that there was a feed- 

 back, and there can t have been in time; I think time doesn't run 

 backwards. 



LYTLE: Not very well, but there is another experiment we have 

 done which further illustrates this point. A group of animals was 

 reared from frustules in the normal way to obtain colonies; then 

 tlie feeding rate was suddenly doubled. In this case there was no 

 significant effect on hydranth and medusa budding, but the produc- 

 tion of frustules doubled. When the feeding rate was again dou- 

 bled suddenly, frustule production once more doul:)led, while hy- 

 dranth budding and medusa budding remained unaffected. There- 

 fore, the additional food went only into the production of frustules. 



LOOMIS: We have been growing Cijanca artica in known solu- 

 tion for about eight months and have observed a very similar situ- 

 ation to the one you have described in Craspcdacusta. Thus, we 

 find that they will bud indefinitely if fed every day with brine 

 shrimp and then placed in clean water. They give no hint of form- 

 ing medusae under these conditions. I left one culture in the ice box 

 for a month, however, and then found that it had strobilized and 

 was now giving off medusae. The thing that is pertinent to Dr. 

 Hand's question, I believe, is that the new routine of starvation 

 and stagnation without water change stops l^udding and induces 



