EYES. 236 



derived from the observations of Swammerdam, Leeuwen- 

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

 Schelver. 



Lenses. 



In the ant there are 50 



In the convolvuhis sphinx . . . . 1300 



In the common house-fly . . . 4000 



In the silk-worm moth 6236 



In the goat-moth 11300 



In the di-agon-fly 12544 



In a butterfly 1/355 



In a mordella 25088 



And, according to a calculation cited by Geoffroy, 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 antennge are inserted so close to their in- 

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

 and more or less sm'round the base of the antenna? (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 Hmb 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 fom* composite eyes, which in fact appears to be the 

 case in the whhlwig-beetles {Gyrinus), and in the males of 

 some may-flies {Ephemerce, fig. 66). 



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



