RICHARD L. WOOD 65 



HESS: I've seen mesoglea in very young buds almost immediately 

 after their formation. 



FAWCETT: I have no reason to regard the mesoglea as different 

 from any other epithelial basement membrane except for its greater 

 thickness. Where one has two epithelial or endothelial layers 

 arranged base-to-base in higher forms, one finds a layer of amor- 

 phous, PAS positive material which looks very much like a thin 

 mesoglea. I've always found this a very attractive prospect in 

 hydra research. Perhaps here is the best place to study the structure 

 and properties of basement membranes, and we might gain informa- 

 tion from the mesoglea that could be carried over to the basement 

 membranes which are such physiologically important structures in 

 higher forms. 



I would ask you a question on terminology. I wonder why you 

 choose not to call these specialized zones of attachment "terminal 

 bars"? I certainly agree with you that "desmosomes" is preferable 

 from every point of view to the term "attachment plaques," but 

 isn't there an adequate functional reason for making a distinction 

 between desmosomes and those devices that occur next to the free 

 surface extending for the full length of the cell boundary and 

 which may very well have the function of preventing access of 

 material to the intercellular space. Isn't it desirable to distinguish 

 these elongated structures from the desmosomes which are circular 

 plaques that occur at many points along the confronted surfaces of 

 the epithelial cells and seem to be solely for attachment? 



WOOD: I agree, Dr. Fawcett, but in my own terminology I 

 regard the term desmosomes as a more general term. I then say 

 this is a "terminal bar" type of desmosome. I'm sorry I didn't make 

 it clearer in my presentation. This concept of the generality of the 

 term desmosome comes from Schalfer's original description. I think 

 "Schussleisten," which, of course, was the terminal bar, is an earlier 

 term. Schalfer regarded the terminal bar as possibly arising from 

 fusion of a series of small plaques. I've used the term desmosome in 

 this general sense. I don't feel rigid about it, however. 



HESS: We all try to get hydra fixed in an extended state. Some of 

 the things we see in the mesoglea might be very different, I think, 

 depending on the state of contraction of the hydra. 



