44 THE BIOLOGY OF HYDRA : 1961 



DISCUSSION 



LOOMIS: At what point do interstitial cells start differentiating 

 the four types of nematocysts? 



HESS: I'm sure someone else later in the program could answer 

 that. I have not actually worked on the structure of the nematocyst 

 per se, just the cnidoblast. 



SLAUTTERBACK: Dr. Hess, I'm afraid your fine micrographs have 

 stolen the thunder from the rest of the electron microscopists here. 

 I did not want to raise the issue of what you have called the 

 gland cell. I believe that on the basis of location, staining proper- 

 ties and appearance of the secretory granules in electron micro- 

 graphs, your term includes two distinct cell types as has been sug- 

 gested in the classical literature. We have been calling the cell 

 which is more prominent in the hypostome region and resembles 

 the goblet cell of the vertebrate digestive system, a mucous cell. 

 The other type, which is more prominent below the hypos'come and 

 resembles the pancreatic acinar cell, we have called the zymogenic 

 cell. 



HESS: It seemed to me that these different appearances might be 

 cyclical changes. Most of the cells have light vacuoles and only 

 rarely do some of them stain darker in the electron microscope. 

 I haven't done histochemical staining, and you might be right that 

 two different cell types occur because many people speak of these 

 two kinds of cells. 



BURNETT: I would like to mention some histochemical results 

 we have obtained on regenerating hydra. If the hypostome of the 

 hydra is excised, we find that mucous cells begin to appear in 

 abundance in the gastrodermis at the point of excision about 12-18 

 hours after cutting. The secretory material in these cells is PAS 

 positive, stains with alcian blue, is metachromatic after toluidine 

 blue or methylene blue staining, and is removable by hyaluronidase 

 digestion. This material is most certainly an acid mucopolysac- 

 charide. Gland cells appear six hours after excision. The secretory 

 droplets in these cells are several times larger than those found 

 in the mucous cells. Moreover, gland cells do not stain with alcian 



