- 1:!i; - SENSE ORGANS. 



40. Pain : examine a section through a cornea to see the free nerve-endings 

 at the surface. 



41 . Pressure sense organ : examine the section of a tactile corpuscle, noting 

 the central receptive cells with which the sensory nerve-endings are in contact, and the 

 protective envelope of connective tissue. 



42. Pressure sense organ : watch the small fresh-water annelids carrying out 

 their swaying respiratory movements and notice how this movement is instantaneously 

 stopped by a light tap on the glass vessel. 



