206 



ZOOLOGY 



slowly about in search of food. The tentacles are richly 

 supplied with nettling cells, each of which contains a 

 fluid-filled capsule, in which is coiled a thread-like tube. 



FIG. 192. Sycon gelatinosum. A portion slightly magnified : one cylinder 

 (that to the right) bisected longitudinally to show the central stomach 

 cavity opening on the exterior by the osculum, and the position of the incur- 

 rent and radial canals ; the former indicated by the black bands, the latter 

 dotted, ip marks the position of three of the groups of inhalant pores at 

 the outer ends of the incurrent canals; 6, osculum. 



When stimulated by contact with some foreign body the 

 tentacle closes around it, while from each capsule the 

 lasso-thread rolls out as the finger of a glove is rolled 

 inside out, and discharges the irritating poison through 



