ALLISON L. BURNETT 439 



on to the epidermal batteries of H. pirardi where they are still cap- 

 able of discharging. 



CROWELL: I'm sure cnidoblasts have to migrate and I'm pretty 

 sure we're not yet clear on how they do it. Now another aspect of 

 the same thing. You spoke of inducing interstitial cells in the basal 

 region. Were these cells there, or did they move in? 



BURNETT: The interstitial cells migrated from more distal re- 

 gions of the animal. I am almost certain of that. 



CROWELL: Did they invade by way of the gastrovascular tract, 

 or did they creep? What happens when they get there? 



BURNETT: I don't think interstitial cells ever migrate via the 

 gastrovascular cavity. Brien has studied interstitial cell migration 

 from a small portion of normal hydra grafted to a hydra whose 

 interstitial cells were killed through X-irradiation. He observed an 

 epidermal migration of interstitial cells. We have noted a similar 

 phenomenon in our induction experiments. 



CROWELL: Were they creeping? Are they wriggling between 

 epidermal cells? 



BURNETT: I've never seen them creep. I suppose they migrate 

 in an amoeboid fashion. I have never seen interstitial cells in the 

 gastrodermis at any stage during the induction phenomenon. 



CROWELL: I think Nelson Spratt has seen migrating cells work- 

 ing their way along. Were they interstitial cells? 



FULTON: No, they were nematoblasts, l^ut Dr. Spratt made 

 his observations on Tubiilaria. 



BURNETT: I'm not sure that undifferentiated cells are capable 

 of migrating. I am referring to the small basophilic cells seen in 

 nests along the length of the epidermis. Each time that I observe a 

 "migrating cell" it is much larger than the cells found in these epi- 

 dermal nests. Perhaps a "migrating cell" is a partially differenti- 

 ated interstitial cell. 



FAWCETT: It seems to me that these cells can only migrate at 

 either end of this differentiation sequence. They could migrate 



