106 



COLLEGE ZOOLOGY 



Nemafocysts 

 on tentacle 



Hypostome 



Epidermis 

 Interstitial cells 

 Gastrovascular cavity 



Testis 

 Gastrodermis 



Longitudinal and 

 circular muscles 



rmis- 



Nerve network 

 Egg in ovary 



Cross section 



Bud 

 Mesoglea 



Basal disk 



Aboral pore 

 Closed Open 



Figure 51. Hydra. Parts cut away and sections to show structure. (Redrawn from a drawing 

 by Justus F. Mueller; prepared exclusively for this text.) 



adjacent cells. These are the mucous gland 

 cells. Their contractile fibers form the 

 sphincter around the mouth, and they assist 

 in swallowing food and in preparing it for 

 digestion. 



Whereas the nutritive cells rest on the 

 mesoglea, the gland cells are tear-shaped and 

 wedged in between the free ends of the 

 nutritive cells. These gland cells occur 

 abundantly in the stomach and in the hy- 



