ARTHUR HESS 45 



blue and are not metachromatic, but positive to Millon's reaction 

 for proteins. These two types of cells are, therefore, quite different 

 from one another both histochemically and morphologically. 



I have a question. Were the cnidoblasts in the same cluster 

 forming the same type of nematocysts? 



HESS: I didn't notice the type of nematocyst, but all those within 

 a cluster seem to be in the same stage of development. 



FAWCETT: I would like to comment on that point. It has been 

 our experience that within any single cluster of cnidoblasts, they 

 are all forming nematocysts of the same kind. They are also pre- 

 cisely synchronized in their development. I would comment further, 

 if I may, on the syncytial relationship that was mentioned. I noticed 

 in Dr. Hess' pictures two distinct kinds of syncytial relationships. 

 In a number of instances, the connections between cells appeared 

 simply as small discontinuities of varying lengths in the pairs of 

 membranes constituting the boundaries between cells. We have 

 seen such apparent communications, but although our technique 

 was seemingly good enough to make it unlikely that these were 

 artifactitious breaks in the continuity of the cell membranes, this 

 has nevertheless always been a disturbing possibility. There is an- 

 other kind of syncytial relationship between cnidoblasts which is 

 clearly not artifactual, and is of considerable interest in relation 

 to the mechanism of cell division and the control of differentiation. 

 It is this kind of intercellular bridge, found in both interstitial 

 cells ( Fig. 1 ) and cnidoblasts ( Fig. 2 ) , that I would like to illustrate 

 in order to emphasize the special nature and probable significance 

 of the syncytial relationship between cnidoblasts. Groups of eight 

 or sixteen cells arising by proliferation from a single interstitial 

 cell remain connected by bridges a micron or so in diameter, en- 

 closed by a specialized, thickened area of membrane that has a 

 characteristic contour. There is no possibility that this localized 

 thickening of the plasmalemma and special configuration of the 

 sin-face could arise as an artifact of specimen preparation. Notice 

 the heartshaped outline of the intercellular space and the definite 

 ridge that encircles the waist of the intercellular connection. Dr. 

 Slautterback and I believe that such bridges arise during division 

 of the interstitial cells when the constricting cleavage furrow en- 



