HYDRA 79 



Which of the layers of the body is involved in the form- 

 ation of the reproductive organs? Make drawings. 



III. Sections of the Body. 



On the slides are thin sections of the body cut transversely, 

 that is at right angles to the long axis of the body. These 

 sections have been colored to render them more distinct. 

 Distinguish the ectoderm and entoderm. How are they 

 separated ? How does the supporting layer which separates 

 them differ from the ectoderm and entoderm? Is the 

 ectoderm of uniform thickness? Note shape, size and con- 

 tents of the cells. At the inner ends of the cells may some- 

 times be found muscular prolongations of the ectoderm 

 cells. Between the bases of the ectoderm cells are smaller 

 cells not extending to the surface. These are interstitial 

 cells and from them arise the nematocysts and the repro- 

 ductive cells. 



Compare the cells of the entoderm with those of the 

 ectoderm in shape, size and contents. Look for gland cells 

 in the entoderm. These will appear as more deeply stain- 

 ing cells between the ends of the cells which border on the 

 enteron ; they secrete digestive enzymes. 



Draw a portion of the section much enlarged showing, 

 especially, the cell structure. 



