504 EXTERNAL ANATOMY OF INSECTS. 
which he ascertained that the stemmata, as well as the 
compound eyes, were organs of vision. He first smeared 
the Jatter 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?. 
From this experiment it seems as if the compound eyes 
were for horizontal sight, and the stemmata for vertical. 
The definition of them by Linné 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. 
Though a large number of insects have them, they are 
by no means universal, since some Orders, as the S¢re- 
psiptera, Dermaptera, and Aptera, are altogether without 
them. The Coleoptera, also, have been supposed to afford 
no instance of species furnished with them; but in the 
fourth number of Germar and Zincken Sommer’s Maga- 
sin, it is affirmed that they are discoverable in Graven- 
horst’s genus Omalium, but not in the kindred genera 
2° Reaum. v, 237—. 
