SEARS CROWELL 313 



evidence for mitosis in these growing tips is most unsatisfactory. 

 Berrill says mitosis occurs in growing hydranths but he never pre- 

 sents any illustration of this mitotic activity. This is one reason why 

 Mr. Lunger is now trying to look at these growth zones using the 

 electron microscope. We hope to understand these processes at the 

 cellular level. We certainly cannot right now. 



STREHLER: At the end of this afternoon's session I hope to 

 show some time-lapse movies of an irradiated colony. I call this 

 movie "On the Beach." 



FULTON: Can I interject something? I have been trying very 

 hard to find out where cell division occurs in Cordylophora. I 

 don't know whether it's me or the animal, but I cannot see any 

 chromosomes. If anybody knows how to see mitosis in adult hy- 

 droids I would be very happy to hear of it. 



CROWELL : Send me a copy of the letter. 



LYTLE: The only place we have been able to find mitotic figures 

 in Cordylopliora is in early embryos. 



FULTON: This is easy. 



LYTLE: Not as easy as one might expect. We had to look at a lot 

 of sections to find any mitotic figures. 



FULTON: Adult tissues must divide for they grow about one- 

 tenth of a millimeter an hour. There must be cell division some- 

 where. 



SLAUTTERBACK: In reference to the transected bud, I was 

 quite interested in your "rob Peter to pay Paul" expression. I 

 take this to mean that any one cell possesses not just a single pat- 

 tern of differentiation, but all the possible patterns necessary for the 

 production of a whole hydranth. And in this case, a cell may car- 

 ry out each of these patterns sequentially until it has gone through 

 all the steps normally carried out by many different cells. Do 

 I understand correctly, or is there some mitosis going on and it is 

 the daughter cells which make tentacles where the parent cell has 

 made perisarc or stem or something else? 



CROWELL : I don't think we know. 



