EXTERNAL ANATOMY OF INSECTS. 505 



have a cornea, and what he takes for the uvea a ; and the 

 latter has supposed that the compound eyes and these 

 simple ones have, the one the power of magnifying ob- 

 jects much, and the other but little, so that the former 

 are for surveying those that are distant, and the latter 

 those that are near b . The same author relates some ex- 

 periments that he tried with the common hive bee, by 

 which he ascertained that the stemmata, as well as the 

 compound eyes, were organs of vision. He first smeared 

 the latter over with paint, and the animals, instead of 

 making for their hive, rose in the air till he lost sight of 

 them. He next did the same with the former, and placing 

 the bees whose stemmata he had painted within a few 

 paces of their hive, they flew about on all sides among 

 the neighbouring plants, but never far : he did not ob- 

 serve that these ever rose in the air like the others c . 

 From this experiment it seems as if the compound eyes 

 were for horizontal sight, and the stemmata for vertical. 



The definition of them by Linne and Fabricius as 

 smooth, shining, elevated or hemispheric puncta, con- 

 veys a very inadequate idea of them ; for, except in a 

 very few instances, they are perfectly clear and transpa- 

 rent, and their appearance is precisely the same as that 

 of the simple eyes of Arachnida &c, under which head 

 they might very well have been arranged ; but as the last 

 are primary eyes, and the stemmata secondary, it seemed 

 to me best that they should stand by themselves. The 

 structure of both is probably the same, and their inter- 

 nal organization that of one of the lenses of a compound 

 eye, and both are set in a socket of the head. 



a Bibl, Nat. i. 214. b Reaum. iv. 245. 



c Ibid. v. 287—. 



