Mr Ewing on the Structure of' the Eyes of Insects. 299 



may either be a reflection, or it may be the dark orbicular side 

 of the ball above-mentioned, shining through the limpid gummy 

 liquor into which it floats. There are no lenses in the lace- 

 like covering of the eyes of this insect, but they are lined with 

 a thin transparent membrane betwixt the external covering 

 and coating of the eye. 



The eye of the night butterfly, or moth, has the same struc- 

 ture as the one just described, only it is dark when viewed 

 in the light, but if examined in the shade, it shines with a 

 beautiful yellowish lustre. This is emitted from the ball of 

 the eye after being extracted from the insect. There is a pe- 

 culiarity in the eye of this insect which I cannot find in any 

 other I have examined ; viz. from the hexagons in the exter- 

 nal covering proceed tubes which convey the apertures through 

 the dark coating of the eye. They are smallest next the ball, 

 are hard and transparent, and appear to be of the same sub- 

 stance as the external covering. There are no lenses in the 

 covering of the eye of this insect. 



The next modification of compound eyes belong to a very 

 numerous class of insects of the fly kind, (and it is to this 

 class chiefly I think the term can be applied ;) viz. to all those 

 which are provided with stemmata, (a kind of eyes which I 

 shall next mention.) As I have not been able to discover the 

 effect of these as organs of sight, I shall merely state, that, in 

 all those appendages called compound eyes in insects having 

 stemmata, I could never find lenses, nor any internal organi- 

 zation similar to those that have them. 



Stemmata. 



These are eyes with which the greater number of bees and 

 flies are provided, and they appear to be their real eyes. They 

 are exactly similar to, and capable of the same properties as 

 simple eyes ; they are variously situated in various insects, but 

 in all of them which I have tried, if they are shut up, the in- 

 sect is rendered blind. 



In the foregoing remarks, I have merely mentioned the 

 result of many experiments, from which I have preserved spe- 

 cimens of various eyes, which prove the facts stated ; and since 

 the oculi of insects arrange themselves under three different 



