384 



THE BIOLOGY OF HYDRA : 1961 



contracted somewhat. The huge vacuoles in the gastrodermal cells 

 are diminished or absent. These acid phosphatase positive granules 

 are of very uniform size. 



Figure 9 is an electron micrograph of a regressing hydranth 

 (taken in collaboration with Dr. David Brandes of the Pathology 

 Department, Baltimore City Hospitals) and shows the complete 

 intracellular disorganization which takes place during this process. 

 An occasional mitochondrion still seems to have a few cristae intact 

 but the high degree of vacuolization and lamination in this section 

 is completely foreign to the normal anatomy of this organism. 





Fig. 10. Accumulation of acid phosphatase-positive granules in the tips 

 of the tentacles of Hydra. Gomori stain. 500X. (From Brock and Strehler, un- 

 published). 



For comparison in the succeeding figures, evidence of acid 

 phosphatase activity in certain interesting regions of Hydra is pre- 

 sented. Note the gradient of increasing acid phosphatase activity 

 as one moves toward the tips of the tentacles. This activity is con- 

 fined to the gastrodermal cells of the tentacle tips (Fig. 10). 



In the base, one also finds acid phosphatase activity in the pre- 



