404 Dr. Sharp's account of recent experiments 



hymenopteron continues to direct itself towards it, 

 evidently without perceiving it, or, at any rate, without 

 perceiving it distinctly, until the insect's hody, or a 

 portion of its body, has penetrated into the shadow. 

 Instantly the insect receives a general impression (im- 

 pression that may be either dermatoptic or visual, 

 possibly both) ; it then hesitates for a very brief instant, 

 then alters its course in a right angle, makes literally a 

 half-turn to the right or to the left, proceeds parallel to 

 the outline of the shadow, then again resumes its course 

 towards the source of light, making again a similar 

 change of direction when it again passes into the shadow 

 of a fresh obstacle." 



Thus he concludes that Hymenoptera are largely 

 guided by sensations arising from the distinctions be- 

 tween light and shade. 



After describing a number of other observations on 

 insects and on Vertebrata, these latter made for the sake 

 of comparison, Prof. Plateau passes to the account of 

 his last series of observations. 



Pakt V. 



a. The perception of movements in insects, b. Supplement 

 to the experiments on the flight of insects rendered 

 blind, c. General summary. 



He reminds us that if we walk about in a field or 

 garden the insects fly from us in all directions, but that 

 if we stand still they are no longer frightened, and not- 

 withstanding our presence pursue their occupations. 

 Thus w^e may conclude that it is our movements, not 

 our bodies, that they perceive. If movements are made 

 slowly he found that after gaining some experience he 

 was able to actually touch insects with his finger once, 

 twice, or even oftener, without disturbing them. He 

 accordingly made a series of observations and tabulated 

 the results, so as to show the distance at which insects 

 perceived the movements of the body or arm of the 

 observer, and whether they allowed themselves to be 

 touched or not. Commencing with Hymenoptera, he 

 gives a list of 28 species, and found that they perceived 

 movement at a distance which on an average may be 

 said to be about eighteen inches or two feet, and all the 



