96 



MANUAL OF ZOOLOGY 



SECT. 



the four-sided mouth (mfh}. Very commonly as the medusa 

 swims the umbrella becomes turned inside out, the sub- 



f^cnb 

 ^^ att n " 



crib 



FIG. 42. Nematocysts of hydra. A, undischarged; B, discharged; C, nerve- 

 supply; cnb, cnidoblast; cnc, cnidocil; u/t, nucleus; ntc, nematocyst; nv.c t 

 nerve-cell. (From Parker's Biology, after Schneider.) 



umbrella then forming the convex surface, and the manu- 

 brium springing from its apex (Fig. 41, C). 



