96 



MANUAL OF ZOOLOGY 



SECT. 



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

 swims the umbrella becomes turned inside out, the sub- 



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

 supply; cub, cnidoblast; cnc t cnidocil ; nn, nucleus; ntc, nematocyst ; uv.c, 

 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). 



