EYES. 235 



derived from the observations of Swammerdam, Leeuwen- 

 hoeck, Andre, Baster, Reaumur, Lyonnet, Goetz, Puget, and 

 Schelver. 



In the ant there are . . . . 50 



In the convolvulus sphinx . . . . 1300 

 In the common house-fly . . . 4000 



In the silk-worm moth . .... 6236 



In the goat-moth 11300 



In the dragon-fly 12544 



In a butterfly 1/355 



In a mordella 25088 



And, according to a calculation cited by Geoffrey, there 'must 

 be not less than 34,650 of such facets in the eye of a butter- 

 fly. When one of the eyes is detached from the head and 

 cleaned, the lenses are found to be as clear as crystal. 

 Reaumur fitted one of them thus removed to a lens, and found 

 that he was able to see through it distinctly, the object being, 

 however, greatly magnified. Ordinarily the eyes are entire, 

 but sometimes the antennae are inserted so close to their in- 

 ner margin that the eyes are thrown out of their ordinary form, 

 and more or less surround the base of the antennae (fig. 63). 

 Sometimes even the eye is thus completely divided into two 

 parts by the antennae being inserted in the middle (fig. 64). 

 The same thing occurs in both respects, when the lateral 

 margins of the head become acute, in which case they enter 

 the anterior limb of the eye, and either partially, as in Dorcus 

 (fig. 65), or entirely, divide it in two parts ; thus forming an 

 upper and an under eye : hence these insects may be said to 

 have four composite eyes, which in fact appears to be the 

 case in the whirlwig-beetles (Gyrinus), and in the males of 

 some may-flies (Ephemerae, fig. 66). 



Ordinarily the eyes are sessile, that is, attached by their 



