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116 



BIOLOGY: GENERAL AND MEDICAL 



fife 



FIG. 41. Hydra. A, Vertical section of the entire animal, showing the 

 body wall composed of ectoderm (ect) and endoderm (end), enclosing an enteric 

 cavity (ent. cav), which, as well as the two layers, is continued (ent. cav') into 

 the tentacles, and opens externally by the mouth (mth) at the apex of the 

 hypostome (hyp). Between the ectoderm and endoderm is the mesogloea (msgl), 

 represented by a black line. In the ectoderm are seen large (ntc) and 

 small (ntc') nematocysts; some of the endoderm cells are putting out pseudopods 

 (pad), others flagella (fl). Two buds (bd l , fed 2 ) in different stages of development 

 are shown on the left side, and on the right a spennary (spy) and an ovary (ovy) 

 containing a single ovum (ov). B, portion of a transverse section more highly 

 magnified, showing the large ectoderm cells (ect) and interstitial cells (int. c); 

 two cnidoblasts (cnbl) enclosing nematocysts (ntc), and one of them produced 

 into a cnidocil (cnc) ; the layer of muscle processes (m.pr) cut across just external 

 to the mesogloea (msgl); endoderm cells (end) with large vacuoles and nuclei 



