Journal 



OF THE 



NEW-YORK MICROSCOPICAL SOCIETY. 



Vol. I. FEBRUARY, 1885. No. 2. 



COMPOUND EYES AND MULTIPLE IMAGES. 



BY J. D. HYATT. 



(^Presented January 2d, 1885.) 



My microscopical recreations the past summer were directed 

 mainly upon the structure of the compound eyes of insects, not 

 so much for a definite scientific purpose, as with the practical 

 object of discovering what insects have eyes that are the most 

 serviceable for showing multiple images under the microscope. 

 The results thus far obtained are far from exhaustive ; yet I 

 have fallen upon some curious features in the structure of these 

 organs, which may possess the interest of novelty to an audience 

 not composed exclusively of entomologists. 



These compound eyes, consisting externally of a great number 

 of lenses, sometimes exceeding twenty thousand, set in a frame- 

 work of convex or, often, hemispherical form, have a range of 

 vision, or "angular aperture," very much larger than could be 

 commanded by a simple eye of the same convexity. For, while 

 the simple eye could form correct images of those objects only 

 which are situated within the range of rays passing through its 

 optical axis, the minute lenses composing the compound eye 

 may, many of them, receive light from a horizon as low down as 

 the base of the entire set, if not lower. 



In some species of Neuroptera the head is nearly cylindrical, 

 and is placed with its axis transverse to the axis of the insect's 

 body. As the eyes, constituting, of course, the extremities of 

 the cylinder, have a diameter exceeding that of their support, 

 and are, besides, hyperhemispherical, they give to the head the 

 appearance of a dumbbell. Were one of these insects placed at 

 the centre of a hollow sphere, it could, undoubtedly, see at the 

 same moment every point of the sphere's interior surface. 



The Gyrinus, or Water-beetle, which may be seen sporting on 

 the surface of still water in summer, has the unusual number of 



