74 THE BIOLOGY OF HYDRA : 1961 



bi-polar and tri-polar neurons of the epidermis. Those in the gastro- 

 dermis possess extremely long proeesses which branch profusely 

 (Fig. 2). She has suggested to me that perhaps the epidemial 

 net serves to coordinate the fast contraction of the longitudinal 

 fibers, and the neurons in the gastrodermis control the slower 

 contracting circular muscle fibers. She has been able to find sensory 

 cells both in the epidermis and gastrodermis. I have been able to 

 consistently demonstrate an epidermal nerve net by simply fixing 

 a whole hydra for Yi hour in 100% alcohol and then staining for a 

 few minutes in 0.1"? methylene blue. The nerve set is especially clear 

 in the transparent areas of the tentacles and peduncle. If this 

 interlacing network of bi-polar and tri-polar cells is not a nervous 

 system then morphologically it is a unique system in the animal 

 kingdom and one that must be reckoned with. Personally, I 

 feel certain it is a nerve net. 



Fig. 2. Isolated gastrodermal nerve cell (Semal Van-Gansen). 



HESS: Couldn't these "nerve cells and fibers" be cell membranes 

 radiating out from the intercellular spaces? Do the intercellular 

 spaces stain? This is a dissection, is it not? 



BURNETT: Yes, this is a dissection. 



HESS: Well, the cell membranes could be left intact radiating 

 from intercellular spaces filled with extensions of mesogleal sub- 

 stance. Impregnation of these elements could yield a picture appear- 

 ing like nerve cells and fibers. 



