EXPERIMENTS ON VISION OF INSECTS. 173 



make but a small angle with one another. Lowne has 

 calculated that wasps, humble bees, dragon-flies, etc , 

 would, at a distance of twenty feet, be able to distinguish 

 objects from half an inch to an inch in diameter. Thus 

 a dragon-fly would see an object twenty feet from its 

 eye iti tlie same detail that a man would perceive it at 

 a distance of a hundred and sixty feet. 



Moreover, when Clapaiede * observes that bees will 

 return from a considerable distance straiglit to the door 

 of their nest, and that, under Miiller's theory, the door 

 would at such a distance be absulutely invisible, he 

 forgets that the bee first probably guides itself by the 

 known position of the door in relation to some tree or 

 other large object, then with reference to the hive 

 itself, and that it is quite unnecessary to assume that 

 the door is actually seen from a distance. 



With reference to the power which insects possess 

 of determining form, Plateau t has recently made some 

 ingenious experiments. Suppose a room into which 

 the light enters by two equal and similar orifices, and 

 suppose an insect set free at the back of the room, it 

 will at once fly to the light, but the two openings 

 being alike it will go indifferently to either one or the 

 other. That such is the case Plateau's experiments 

 clearly show, and, moreover, prove that a comparatively 

 small increase in the amount of light will attract 

 the insect to one orifice in preference to the other. It 

 occurred then to Plateau to utilize this by varying the 

 form of the opening, so that the light admitted being 



* "Zur Morph. der zus. Augen bei den Arthropodeu," Zsit. filr 

 Wiss. Zool., 18G0. 



t Bull, de I'Acad. Hoy. de Belgique, t. x., 1885; Comptes Rendus de 

 la Soo. Ent. de Belg., 1887; " Eech. Exp. sur la Vision cliez lea 

 Arthropodes," 1887. 



