IV 



PHYLUM CCELENTERATA 



127 



openings of a pair of canals given off from the enteric cavity. 

 Between the two excretory pores is a remarkable structure, 

 which is the nerve-centre as well as an organ of special 

 sense. The mouth leads into a flattened tube, the gullet, 

 and this again leads into a cavity, the infundibulum, which 



ad.c 



ad.c. 



s c 



B 



FIG. 66. Hormiphora plumosa. A, transverse section of one of the branches of 

 a tentacle; B, two adhesive cells (ad c,~) and a sensory cell (j. c) highly magni- 

 fied, cu, cuticle; , nucleus. (After Hertwig and Chun.) 



probably corresponds to the stomach of the sea-anemone. 

 From this cavity certain canals are given off. 



Stinging-capsules are not developed, their place being 

 taken by a number of peculiar cells called adhesive cells, with 

 which the branches of the tentacles are covered. An 

 adhesive cell (Fig. 66, B) has a convex surface, produced into 

 small papillae, which readily adheres to any surface with 

 which it comes in contact, and is with difficulty separated. 

 In the interior of the cell is a spirally coiled filament, the 

 delicate inner end of which can be traced to the muscular 

 axis of the tentacular branch. These spiral threads act as 

 springs, and tend to prevent the adhesive cells from being 



