1887.] NEW-YORK MICROSCOPICAL SOCIETY. 43 



The following extract from an article by M. A. Forel, in Rec. 

 Zool. Suisse, iv. (1886) pp. 1-50, published in the Journ. Royal 

 Micros. Soc, June, 1887, p. 379, will be of interest, in connec- 

 tion with the article by Mr. Riederer, in this number of this 

 Journal. 



Vision of Insects. — M. A. Forel gives an account of past 

 and recent experiments on the vision of insects, and sums up 

 the conclusions as follows : — 



(i) Insects direct themselves in flight almost wholly, and on 

 the ground partially by means of their facetted eyes. The an- 

 tennae and buccal sensory organs cannot serve for directing 

 flight. Their extirpation makes no difference. 



(2) J. Miiller's mosaic theory is alone true. The retinulje of the 

 compound eyes do not each receive an image, but each receives 

 a simple ray more or less distinct in origin from that of its 

 neighbors. Gottsche's theory is false. (Miiller, Grenacher 

 Exner.) 



(3) The greater the number of facets, the more elongated the 

 crystalline cones, the more distinct and the longer the vision. 

 (Miiller, Exner.) 



(4) Insects can see particularly well the movements of bodies, 

 and better during flight than when at rest, the image being dis- 

 placed in relation to the eye (Exner). This perception of the 

 mobility of objects diminishes as the distance increases. 



(5) Contour and form are only indistinctly appreciated, and 

 the more indistinctly the fewer the facets, the shorter the crys- 

 tallines, the farther and smaller the object. Insects with big 

 eyes with several thousand facets can see with tolerable 

 distinctness. 



(6) In flight, insects can by means of their compound eyes 

 appreciate with accuracy the direction and distance (not too 

 great) of objects. When at rest they can also estimate the 

 distance of fixed objects. 



(7) Certain insects (bees and humble-bees) can clearly dis- 

 tinguish colors, and that better than form. In others (wasps) 

 the perception of color is very rudimentary. Ants perceive the 

 ultra-violet rays (Lubbock). 



(8) The ocelli seem to furnish only very incomplete vision, 

 and to be simply accessory in the insects which possess also 

 compound eyes. 



