1448 THE STORY OF THE UNIVERSE 



you will see just in front of the point where they sep- 

 arate and their front outlines diverge a minute cres- 

 cent-shaped cushion of a pale-green color, at each 

 angle of which is a minute antenna. Close to the base 

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

 head that divides the green crescent from the com- 

 pound eyes, a globose 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. The shining 

 glassy hemisphere is a cornea of hard transparent 

 substance, 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 col- 

 ored 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-fly, in a triangle. 



