ISO Discoveries of Milllcr arid others in the 



all the internal parts of the eye, and between 

 the two eyes it is elongated to a point both 

 anteriorly and posteriorly. (Jig. 19. a.) It ex- 

 tends a little over the front surface of the vitre- 

 ous body, and so forms a kind of pupil, whose 

 diameter is greater than that of the lens, and is 

 nearly equal to three fifths of that of the vitreous 

 body itself. 



The whole of the posterior surface of the vitreous body is 

 in immediate contact with the retina ( fig. 18. e\ which is 

 membranous throughout, and towards its centre forms a 

 conical projection continuous with the optic nerve j^ This cone 

 of the optic nerve, the external surface of the retina, the mar- 

 gin of the vitreous body in front, and the internal surface of 

 the integuments, where they are continuous with the cornea, 

 are all covered by the choroid membrane, with its bluish 

 black pigment. 



Besides these two large eyes, the scorpions have, in the 

 middle of the cephalothorax, other and much smaller ones, 

 generally six in number, and similar in their external appear- 

 ance to the stemmata of insects. 



The S'colopendra morsitans has four simple eyes on each 

 side of the head ; three are round, and the fourth, larger in 

 size than the others, is elliptical. The convexity of these eyes 

 is very great. The lenses are hard, transparent, amber- 

 coloured, convex on both sides, nearly round, and large 

 enough to be seen with the naked eye ; the lens of the ellip- 

 tical eye is larger than that of the others, and is elliptical. 



The vitreous body, if it 



exists, is extremely small. 



Fig. 20. represents the 



lenses of the eyes of the 



iScolopendra morsitans, 



magnified, as they appear 



at their under surface, when 



they are removed, though 



still attached each to its 



cornea. Fig. 21. gives a magnified view of the cup-shaped 



black pigment and retina of each of the three round eyes, 



with their optic nerves. 



The number of simple eyes, or stemmata, in the perfect 

 insects provided with them, is generally three ; the dimen- 

 sions of these organs vary much even in different species of 

 the same genus ; in some of the smaller species of Gryllus they 

 are of extraordinary size. 



The stemmata of insects are always convex on the surface. 



