96 



MANUAL OF ZOOLOGY 



the four-sided mouth (mth). Very commonly as the medusa 

 swims the umbrella becomes turned inside out, the sub- 



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

 supply; crib, cnidoblast; cue, cnidocil; tut, nucleus; jrtc, 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). 



