DISCUSSION ON NERVOUS SYSTEM 73 



Dr. Spangenberg used a methylene blue \'ital staining procedure, 

 with a neutral red counterstain, to demonstrate the nerve cells in 

 intact Hydra. I refer you to her recent publication (Spangenberg 

 and Ham, 1960, /. Exp. Zool. 14S, 195-202) for detailed descrip- 

 tions. 



I obser\ ed many of Dr. Spangenberg's methylene blue prepara- 

 tions under phase contrast, and can report that they compare very 

 closely to Dr. Mackie's silver preparations. Nerve cells with from 

 one to seven fibrous processes were observed with interconnecting 

 fibers between many cells. While a complete nerve net could not be 

 stained all at once in any one animal, ner\'e networks in all regions 

 of the bod)- were seen in various specimens. 



As Dr. Mackie reported, cnidoblasts are often found in close 

 contact with ner\'e cells. This doesn't indicate necessarily that there 

 is innervation of the cnidoblast, but the frequency of coincidence 

 is suggestive of that. 



Dr. Spangenberg also identified multi-polar cells with the dis- 

 tinct morphology of neurons in Hydra preparations dissociated 

 into single cells with Hertwig-Schneider fluid. 1 think there is little 

 doubt that nerve cells and a nerve net do exist in Hydra. 



HESS: If one wanted to be skeptical, it might be said that the 

 "nerves" that the Texas group shows associated with the cnidoblasts 

 are the discharged tubes of nematocysts. 



BURNETT: I have recently received some photographs from 

 Semal Van-Gansen at the University of Brussels. She has dissected 

 out nerve elements from hydra with a fine needle. In the epider- 

 mis she finds the typical nerve net described by Hadzi (Fig. 1). In 

 the gastrodermis she does not find a net. Instead she finds a more 

 sparse distribution of nerve cells which do not resemble the small 



Fig. 1. Isolated epidermal nerve cell (Semal Van-Gansen) 



