398 



GENERAL ZOOLOGY 



Fig. 226. — Mnemiopsis, a ctenophore with lobes in place of tentacles. A, 

 side view; B, aboral side; C, oral side, showing the mouth as a small opening in 

 the center. 



N -4 



B 



M 



Fig. 227. — A diagrammatic dissection of Hormiphora, a ctenophore; the 

 ectoderm is dotted, the endoderm striated, and the mesoderm solid black, i, 

 infundibulum, the stomach region, which is connected with eight meridional 

 canals one of which is shown beneath the more central row of combs. The infun- 

 dibulum also gives off two stomodaeal canals and two tentacular canals, one of 

 each being shown in the figure. The stomodaeal canal is close to the stomo- 

 daeum, the tube leading from the mouth (m) to the infundibulum. p, excretory 

 pore; s, statocyst; t, tentacle, the one on the left, in longitudinal section, shows 

 the muscular core by which the tentacle may be retracted into the sheath. 

 {Based on Parker and Haswell.) B, adhesive cell from a tentacle. The convex 

 surface is sticky, and the coiled filament acts as a spring to prevent the cell being 

 pulled out when it is attached to prey. The spiral thread is attached at its base 

 to the muscular axis of the tentacle, n, nucleus. (After Hertwig and Chun.) 



