230 THE BIOLOGY OF HYDRA : 1961 



feeding response. At this time we offered the hydra several hun- 

 dred brine shrimp. The hydra readily captured, killed, and ingested 

 the shrimp. 



LENHOFF: I can give some explanation. When a Hydra punc- 

 tures a shrimp, all sorts of new and unknown substances present 

 in the body fluids of the shrimp flow into the media. There is a 

 possibility that these emitted fluids contain substances which en- 

 hance the feeding reflex. In fact, we have some preliminary indica- 

 tions that phospholipids present in serum do just this. Since I think 

 that the initial activation takes place on the cell membrane, it is 

 possible that the phospholipids act there. 



BURNETT: I suppose it is enhancing something already present. 



LENHOFF: Yes. The point I want to emphasize is that it is very 

 hard to know what is happening since you do not know what is 

 present in the fluids coming out of the shrimp. So many factors 

 affect the feeding reflex, as I have shown you already. 



Chandler Fulton also shows that Cordylophora respond some- 

 what to shrimp after they no longer respond to proline. This may 

 be a similar phenomenon. 



GOREAU: Have you tried amino acids? I ask because we recently 

 noted that small amounts of methionine caused corals to extrude 

 mesenterial filaments. The entire colonies become covered with 

 tangled white masses of filaments that stayed out as long as the 

 methionine (2 /xglO ml) was in the medium. Extrusion of masen- 

 terial filaments is a typical response of some corals when feeding 

 in the presence of thick plankton swarms, but I have never seen 

 such a strong sustained reaction with other stimulants, including 

 clam juice, as with methionine. 



LENHOFF: I haven't tried methionine, although I doubt whether 

 it would cause Hydra to respond. I fully agree that other com- 

 pounds may work on other organisms. Fulton, for example, has 

 shown that proline activates the feeding reflex of Cordylophora. 



GOREAU: Glutathione seems to have little effect on those corals 

 on which it was tried. Zooplankton swarms probably secrete detec- 



