ARTICULATA. 137 
These have been enumerated in various insects, and it has been ascertained 
that in the eye of an ant there are fifty lenses, in a dragon-fly twelve 
thousand, and in various butterflies from six to thirty thousand. The form 
of a compound eye is round, oval, or kidney-shaped, in the last case fre- 
quently receiving an antenna in the concavity. The eyes often nearly 
cover the entire head, extending upwards to bring their inner margins in 
contact, so that the greater part of the surface of the head has the function 
of a vast compound eye, as in the dragon-flies (Zzbellula). In some insects 
the eyes of the male cover more of the head than those of the female. 
Although there is usually but one eye upon each side, this is sometimes 
divided, as in the flat water insect of the genus Gyrznus, in which half of 
the divided eye is above and half below. In Zetraones (meaning four eyes) 
the eyes have been divided by the base of the antenne ; and in some cases 
where they are kidney-shaped, the emargination is so deep that only a 
narrow strip connects the two ends of the eye. The stemmata are three 
(less commonly two, or perhaps even one) lenses or simple eyes, situated 
upon the vertex or forehead, and generally forming a triangle. The 
stemmata are also named ocellz, but as this term is also applied to spots 
resembling eyes (as in the wings of butterflies), the former term is 
preferable. 
The mouth of insects, although composed of the same essential parts, 
has these modified into two principal types of structure, one of which is 
adapted to masticate, and the other to suck food. The former is termed 
mandibulate, and the latter haustellate, and we have the corresponding 
section of insects, Mandibulata and Haustellata ; but in the Hymenoptera 
we find biting mandibles in conjunction with sucking organs. 
In the Mandibulata the mouth organs are as follows: The labrum, or upper 
lip, is a variously shaped horizontal plate, articulated to the clypeus and 
covering the mandibles. The mandzbles, or upper jaws, move laterally and 
horizontally, like scissors. The internal margin is sharp, and often toothed, . 
and the apex is generally curved inwards. The maaille, or lower jaws, 
are situated beneath the former, and have a similar motion, but they are 
less robust. When fully developed, the maxillze are composed of four or 
five pieces, namely, 1, the cardo, or hinge; 2, the stipes. or stalk; 3, the 
squama, or palpifer, closely united with the former, and supporting an 
articulated palpus, or feeler; 4, the mando, or lacinia, which forms. the 
inside of the maxilla, and is clothed with stiff bristles. In the predatory 
Coleoptera its apex is curved, and often articulated, as in Cicindedla 
(pl. 81, fig. 26). 5, the galea, or external lobe of the maxilla, which 
becomes a kind of second or internal bi-articulate palpus in Cicindela. 
In the Orthoptera the galea is large, and articulated at the base, and its 
internal side is concave, so that it approximates and protects the mando, 
whence its name of galea. The mando is often absent, or united to the 
galea, so as to form a single organ. 
The Zabiwm, or lower lip, closes the mouth below, and although it corre- 
sponds with the upper lip, it is a much more beet cuted organ. In some 
points of view it may be compared with a pair of maxillee anitess in a single 
341 
