no 



COLLEGE ZOOLOGY 



tentacles. The interstitial cell in which the nematocyst develops 

 is called a cnidoblast (Fig. 66); it contains a nucleus (nu) and 

 develops a trigger-like process, the cnidocil {one), at its outer end, 



g — 



Fig. 65. — Diagram of a longitudinal section of Hydra, b, bud; b.d, basal 

 disc; bl, blastula; ec, ectoderm; en, entoderm; g, gastrula; gv.c, gastro- 

 vascular cavity; hy, hypostome; m, mouth; m.e, mature egg; m.t, mature testis; 

 «, nematocysts; p. b, polar bodies; /.tentacle; y.e, young egg; y.t, young testis. 

 All the structures shown do not occur on a single animal at one time. 



but is almost completely filled by the pear-shaped nematocyst 

 (nem). Within this structure is an inverted coiled thread-like 

 tube with barbs at the base. When the nematocyst explodes, 



