196 EVEXENTGS AT THE MICKOSCOPE. 



of each antenna there is set in the black skin of the 

 head tliat divides the s-reen crescent from the com- 

 pound ejes, a glohose, polished knob of crystal-like 

 substance, much like the " bull's-eyes" or hemispheres 

 of solid glass that are set in a ship's deck to enlighten 

 the side-cabins. On the front side of the crescentic 

 cushion there is a third similar glassy sphere, but much 

 larger than the two lateral ones. What are these three 

 spherules ? 



They are eyes, in no important respect differing 

 from the individuals which compose the compound 

 masses, except that they are isolated. Tlie shining 

 glassy hemisphere is a cornea of hard transparent sub- 

 stance, behind which is situated a spherical lens, lodged 

 in a kind of cup formed by an expansion of the optic 

 nerve, and which is surrounded by a coloured pigment- 

 layer. 



You may study these simple eyes, or stemmata as 

 they are called, in many other insects, though they are 

 not so universally present as the compound eyes. On 

 the forehead of the Honey-bee they are well seen, as 

 three black shining globules, placed, as in the Dragon 

 lly, in a triangle. 



