Microscopical Essays, 



377 



Mr. Hook computed 14,000 hemifpheres in the two eyes of a 

 drone ; Mr. Leeuwenhoeck reckoned 6236 in a filk- worm's two 

 eyes in it's fly ftate ; 3181 in each eye of a beetle, and 8000 in 

 the two eyes of a common fly. The pearl eyes of the dragon fly 

 appear with a common reading-glafs like fhagrecn, and Mr. 

 Leeuwenhoeck reckoned in each eye of this infect 12,544 lenfes, 

 placed in an hexangular pofition, each lens having fix others 

 round it. He alfo obferved in the center of each lens a minute 

 tranfparent fpot, brighter than the reft, fuppofed to be the pupil, 

 furrounded with three circles, and in appearance feven times lefs 

 than the diameter of the whole lens. Mr. Puget counted 17,325 

 in the eye of a butterfly, which Malphigi concludes to be diftinfct 

 and feparate eyes. The Abbe Catalan, and others, have fmce 

 fhewn, that all the eminences difcoverable in the cornea of infecls 

 have the necefTary parts, and perform the offices of an eye. 

 Leeuwenhoeck difcovered the bundles of optic nerves which ferve 

 thefe imall lenfes ; and Reaumur fuppofes that thefe fupply the 

 place of all that is wanted behind the lenfes, for the organization 

 of an eye complete for vifion, 



But it is in the works of Swammerdam that we are enabled to 

 contemplate the aftonifhing organization of the eyes of infects. 

 Under each mem, or facet, there is a little pyramid of fibres, 

 broad at the bafe, and growing fmaller as it proceeds inwards. 

 The pyramids have the fame number of fides as each eye, and 

 there are, therefore, as many hexagonal pyramids as there are 

 fmall facets, or eyes, in the infecf. An innumerable quantity of 

 pulmonary tubes afcend thefe fibres ; thefe tubes terminate in a 

 fine tranfparent [white fibrous membrane, of a convex lhape, 

 which is alfo thick fet with pulmonary tubes ; under this mem- 



Z z brane 



