CHANDLER FULTON 293 



From my point of view, the major result of this study is that, 

 by reducing the development of a colony to a series of constituent 

 events, it becomes possible to analyze the individual events which 

 give rise to the shape of a colony. Many questions immediately pose 

 themselves. For example, why do upright tubes grow at half the rate 

 of stolon tubes? Why do hydranth-bearing tubes develop only be- 

 hind growing tips, while stolon tubes develop away from these tips? 

 What produces the regular spacing of upright tubes? What de- 

 termines the angle at which each tube leaves its parent tube? As 

 yet, none of these questions has even a preliminary answer, but I 

 hope that at least I have provided you with a more dynamic pic- 

 ture of these hydranth-bearing pipelines. 



REFERENCES 



1. Fulton, C. 1960. Culture of a colonial hydroid under controlled conditions. 



Science 132: 473-474. 



2. Fulton, C. 1960. The Biology of a Colonial Hydroid. Ph.D. Thesis, The Rocke- 



feller Institute, New York. 



3. KiNNE, O. 1958. Adaptation to salinity variations: some facts and problems. In 



Physiological Adaptation ( C. L. Prosser, ed. ) . Washington, American 

 Physiological Society, pp. 92-106. 



DISCUSSION 



MACKIE: Before the discussion turns to the main topics of Dr. 

 Fulton's paper I'd like to comment on the colonial rhythm shown by 

 Cordylophora— the synchronized waves of peristalsis in the hy- 

 dranths. We have also seen this in Dr. Strehler's film of Fennaria. 

 This sort of activity demands a specialized conduction system. Re- 

 cently, R. K. Josephson has recorded action potentials from the 

 stems of Cordylophora and Tuhularia. I cannot give the full details 

 but in Tuhularia there are two rhythmically occurring patterns of 

 activity and one of these patterns has distinct motor effects. 



I'd also like to reiterate that neurons have been identified his- 

 tologically throughout stems and hydranths in Cordylophora, so 

 there's no need for scepticism about the existence of a ner\ous 

 system in these colonial forms. 



