316 THE BIOLOGY OF HYDRA : 1961 



terstitial cells with the electron microscope but not with the light 

 microscope. 



LENHOFF: We measure changes in the number of nematocysts 

 in H. littoralis using a specific test for hydroxyproline, the imino acid 

 that makes up much of the nematocyst capsule. We find that de- 

 capitated Hydra which regenerate complete sets of tentacles show 

 no net increase in hydroxyproline although starved Hydra are able 

 to synthesize this unessential imino acid. Thus, it appears that re- 

 generating animals use the nematocysts that they already have in 

 their body tubes, and no new increase in the number of cnido- 

 blasts occurs by cell division. 



BURNETT: We easily demonstrate mitosis in whole hydra by 

 staining them in methylene blue at pH 7 after first digesting them 

 with ribonuclease (1 mg. ml. for 3-5 hours). The enzyme re- 

 moves all cytoplasmic RNA and makes the hydra more transpar- 

 ent. By simply scanning the surface of the whole animal, one can 

 see nests of interstitial cells in synchronous division. 



MACKIE: I have often seen mitosis in the cell-body part of epit- 

 heliomuscular cells. The fiber part is not affected. It's rather inter- 

 esting in silver preparations because the achromatic figure is chro- 

 matic and the chromatic figures is achromatic. 



WOOD: Couldn't one use radioautography to trace the formation 

 of DNA? This might give an indication of the mitotic rate or turn- 

 over of cells. 



FULTON : If you can figure out how to get labeled thymidine into 

 the animals, I'll be happy to do it. I've tried and seen nothing. 



