INSECTS. 231 
have 25,000. If examined with a microscope, the sur- 
face of these compound eyes appears as you see in Fig. 
181 (p. 230), representing the head and eyes of a bee. 
At a@ are the antenne, and the eyes occupy most of the 
front and sides of the head. The surface is made up of 
hexagonal (six-sided) facets. At A you see them much 
magnified, and at B you see hairs standing out between 
them. Each of these facets is a cornea, or window to a 
little eye. (See “First Book in Physiology,” p. 167.) 
Most insects have these compound eyes, but some have 
only single ones, and some have both, for what reason 
we do not know. 
396. The digestive apparatus is commonly quite com- 
plicated, there being three 
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VAS y stomachs—one correspond- 
bs We 2y ing to the crop of birds, an- 
Fag ‘eee other to the gizzard, while a 
§ ee \ third receives the food and 
mia digests it after it has been 
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softened and ground in the 
other two stomachs. The 
second stomach, or gizzard, 
is often armed with horny 
projections, in order to grind 
up the food effectually. In 
Fig. 182 you have the whole 
digestive apparatus of a 
Beetle. First you see the 
strong cutting mandibles, 
the maxille and the anten- 
ne; then @ the throat, d the 
i gullet, ¢ the crop, d the giz- 
»\\\ zard, e the third stomach, 
J the intestine. The liver, /, 
instead of being such a solid 
‘ig. 182.—Digestive Apparatus of organ 2s it is in vertebrate 
Beetle. and most other animals, is 
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