EXTERNAL ANATOMY OF INSECTS. 493 
contiguous, circular, pellucid lenses, arranged in five 
lines, with another larger behind them, as a sentinel or 
scout, placed at some little distance from the main body. 
In the common millepede (Julus terrestris) there are 
twenty-eight of these eyes, placed in seven rows, and 
taining seven lenses, the next six, and so on, gradually 
losing one, till the last terminates in unity. Each of 
these lenses is umbilicated, or marked with a central de- 
pression. In Craspedosoma, Leach, you will find a similar 
formation. In Armadillo zonatus, a kind of wood-louse 
that rolls itself into a ball, the lenses are arranged in a 
line curved at the lower end, with a single one by itself 
at the posterior end on the outside; they are oblong and 
set transversely, and their white hue and transparency 
give them the appearance of so many minute gems, espe- 
cially as contrasted with the black colour of the animal’*. 
Between these eyes and the antenne is another trans- 
verse linear white body, but opaque, seemingly set in a 
socket, and surrounded by a white elevated line, like the 
bezel of a ring. Whether it is an eye, or what organ, I 
cannot conjecture>. Its aspect is that of a spiracle. 
3. Compound Eyes*.—These are the most common 
kind of eye in hexapod insects, when arrived at their 
perfect state ; in their larva state, as we have seen, their 
eyes being usually simple ?; except, indeed, those whose 
metamorphosis is semicomplete, which have compound 
eyes in every state-—In considering compound eyes, I 
shall advert to their structure, number, situation, figure, 
clothing, colour, and size. 
a Prater XXIX. Fic. 11. h. > Thid. a. 
© Prate XIII, Fie. 10. * See above, p. 117—. 
