66 THE BIOLOGY OF HYDRA : 1961 



LUNGER: I have electron micrographs of Campamilaria endo- 

 derm showing "terminal bar" desmosomes similar to those demon- 

 strated for hydra by Dr. Wood. 



WOOD: This has been observed in several other forms. They 

 appear in planaria, and one is described briefly in Grimstone, 

 Home, Pantin and Robson's publication on Metridium. 



SLAUTTERBACK: I'm willing to call these things "terminal 

 bars," but we must not put a functional significance upon this name 

 because we don't have any way of knowing that these structures are 

 excluding something from the epithelium and preventing it from 

 reaching the mesoglea. As far as I know the only obvious function 

 is attachment, is that right? To put it another way, we should not 

 apply the name terminal bars to the desmosomes of hydra because 

 the function of terminal bars, namely the impeding or preventing 

 the flow of water, electrolytes or other substances between cells, 

 has not yet been proved to exist in any organism or tissue other than 

 mammalian kidney. 



WOOD: I think that the concept of terminal bar involves more 

 than just this concept of separating the lumen from the intercellular 

 space. It is a type of attachment which surrounds the entire surface 

 of the cell. In longitudinal sections it has a bar-like structure which 

 appears dense with certain types of stain. I agree that there is no 

 direct evidence that these specialized desmosomes of hydra func- 

 tion to prevent passage of water or other material intercellularly, 

 but I think that the idea is certainly reasonable because hydra is a 

 fresh water invertebrate and must osmoregulate somehow. There 

 is no kidney to do this and a reduction of exposed cell surface would 

 be one way to improve the situation. 



FAWCETT: There is a piece of evidence not found in hydra 

 which indicates that terminal bars do have the function that has 

 long been attributed to them. In recent work on the proximal con- 

 voluted tubule of the mammalian nephron, Miller found that when 

 he administered hemoglol)in solution to mice, the hemoglobin that 

 filtered through the glomerulus and accumulated in the lumen of 

 the tubule is electron dense and served as a good contrast medium. 

 In electron micrographs one can follow the electron density of the 

 hemoglobin between the cells of the proximal tubule as far as the 



