34 JOURNAL OF THE [February, 



four compound eyes. Besides the usual pair on the upper and 

 frontal part of the head, set in the under side of the head is 

 another pair, looking directly downward and completely sub- 

 merged — "water-immersion" eyes. The utility of this arrange- 

 ment is readily seen. Its anatomy I have not myself examined; 

 but I have somewhere heard or read that the two eyes on each 

 side, though separated externally, are, in a measure, connected 

 internally. The Gyrinus is the only example of this peculiar 

 structure that has come under my observation. 



To those who admire color, a microscopical observation of 

 the eyes of living insects, especially those of the order Diptera, 

 and of the night-flying Lepidoptera, will be fruitful of delight. 

 For the eyes of these insects display an endless variety of colors 

 which vie in brilliancy with the most lustrous of the " bright 

 jewels of the mine." After the death of the insect, however, the 

 color soon disappears. 



In mounting compound eyes for the purpose of showing mul- 

 tiple images, the first step, after carefully washing the interior of 

 the cornea, is to press the cornea flat, so that all the lenses may 

 lie as nearly as possible in the same plane. But as this operation 

 necessarily occasions either a breaking or a folding of the cor- 

 nea, I cut out, with a small punch made for the purpose, a circular 

 disk not larger than can be pressed flat without disturbing the 

 facets. In punching out these disks, a single cutting gives two 

 circular pieces, showing that the cornea is double ; and in the 

 eyes of Cicada, a single cutting gives three separate disks, show- 

 ing a triple set of lenses in the cornea. Each set constitutes, 

 without doubt, an achromatic combination. 



In some of the Diptera, particularly of the genus Tabaims, or 

 Horse-fly, the lenses of the upper and anterior part of the eye 

 are much larger than those situated below a median line. A 

 disk cut from one of these eyes in such a way as to include a 

 number of the upper, or larger facets, and also some of the low- 

 er, is represented in the accompanying diagram. It will be ob- 

 served that the larger facets have, at least, twice the diameter of 

 the smaller, or four times their superficial area. A still more re- 

 markable feature, however, is the difference in focus between 

 the larger lenses and the smaller. For upon placing this part of 

 the eye upon the stage of the microscope, and adjusting the 

 focus for multiple images, I found that the larger lenses form 



