342 Appendix to Proceedings of Royal Physical Society. 



Fig. 1. 



Fig. 2- 



elsewhere considered as prehensile apparatus. These palpo- 

 cils (woodcut, fig. 1) 

 arise each as a some- 

 what rigid process, 

 from the side of one 

 of the large thread- 

 cells buried in the 

 head of the tentacle, 

 and they probably 

 convey an impression Fig x . 

 from bodies coming in- Fig 2 .. 

 to contact with them, 

 to the thread-cell, which causes the extrusion of its dart. The 

 offensive character of the thread-cell, which has been denied 

 (Lewis' " Sea-side Studies" ), is proved by allowing any 

 soft body, as the bulb of a human hair, to touch the tentacles 

 of Hydra, Coryne, or Actinia, when it will afterwards be found 

 studded with their darts buried beyond the barbs. 



thread-cell — b thick palpocil — c surface of head 

 of tentacle. 



tactile corpuscle— b acuminate palpocil— c sur- 

 face of ectoderm. 



