270 THE CANADIAN ENTOMOLOGIST 



only on the elbow joints and membranous coverings of the eye. 

 This lack of spots is explained by assuming that more stimulation 

 is required to excite pain end-organs than pressure end-organs. 



A third theory is that pain end-organs are not distinct from 

 pressure end-organs but are exposed pressure organs situated under 

 unusually thin parts of the epidermis and that pain is not due to 

 any activity of these end-organs b,ut to "a transformation in the 

 gray matter of the spinal cord of nerve excitations conveyed from 

 these exposed pressure end-organs." 



Returning to insects we find that they have well developed 

 nervous systems and that their organs are well supplied with 

 nerve endings. Moreover many insects give signs of discomfort 

 when handled or mutilated. There is no doubt but that they are 

 highly susceptible to pressure stimuli. In fact end-organs of 

 touch such as hairs and bristles are distributed over the entire 

 integument. 



Pain sensations however are hard to distinguish in insects 

 from those of touch. One argues that the mutilated insects 

 heretofore referred to experienced no pain simply because they 

 exhibited no signs of suffering. What then constitutes a symptom 

 of pain in insects? Who is qualified to judge? Many pain racked 

 persons go about their duties without exhibiting any signs of pain 

 other than changes in facial expression. Of course extreme muti- 

 lation of the human body results in almost immediate death while 

 in the case of insects death is not immediate. All pain however 

 is an exhausting experience and injurious to the organism. With 

 insects final exhaustion is simply deferred. 



In the case of the dragonfly eating its own body, it is hard 

 to find a human parallel unless we cite mentally unbalanced 

 persons who inflict serious injuries upon their person. One might 

 argue that they would not do this if it were painful and yet we 

 are positive such actions are painful. 



The character of the insect nervous system is unlike our own 

 and the surface of their bodies is usually rigid and hard and 

 probably not sensitive to pressure and pain in the same way as 

 our own bodies so that we have no reliable guides as to their 

 sensations of pain. Man judges most things by himself and when 

 this guide fails he is at a loss to explain certain happenings in a 



