ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



tentacle into the surrounding water. The most remark- 



the rnidoblast is the nematocyst (nem) which fills up a 



interior. This is a hollow flask or bulb the neck of which 



:i extremely fine tube open at its free end (Fig. 35, C). 



k of the bulb are arranged three sharp blades. 



.is observed within the cnidoblast the fine 



lu [ K I!R- neck with its blades, is turned outside in 



and lies in the interior of the bulb, the tube being coiled 



up int.. a spiral. The rest of the cavity of the bulb is filled 



with fluid, apparently of a virulently poisonous kind. 



lea the nmloblasts such as that which has been. 

 nheil there exist others, more numerous, smaller in size 



en. 



nem 



n. 



B 



FIG. 35. 



Cniclobbst a i. -ts. A, Unextrucled ; B, early stage of extrusion; C, extrusion 



complete, en, Cnidocil ; n, nucleus ; nem, nrm.it 



aematocysts of slightly different shape and unprovided 

 with I.: 



nil 1 (blasts are originally interstitial cells which gradually form 



n tln-ir interior. They then creep away from their 



: ually though not always into the tentacle, burrow their 



mce i>f an ordinary ectoderm cell and there settle 



their .nidocil beyond the surface of the host cell into 



tfater. In a normal ectoderm cell of the tentacle 



:ip or battery of cnidoblasts, a larger one in the 



i -mailer ones round it. 



