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 {L'thelhda). 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 Gyrinus^ in which half of 

 the divided eye is above and half below. In Tdraoms (meaning/bi^?' eyes) 

 the eyes have been divided by the base of the antennae ; 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 ocelli^ 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, Memdlbulata and HausteUata / but in the Hymenoptera 

 we find biting mandibles in conjunction with sucking organs. 



In the Mandibulata the mouth organs are as follows : The lahrum^ or upper 

 lip, is a variously shaped horizontal plate, articulated to the cl3'peus and 

 covering the mandibles. The mandihles^ 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 iinax'dlce^ or lower jaws, 

 are situated beneath the former, and have a similar motion, but they are 

 less robust. When fully developed, the maxillas are composed of four or 

 five pieces, namely, 1, the cardo^ or hinge ; 2, the stipes, or stalk; 3, the 

 sqtiama^ or i)alpifci\ closely united with the former, and supporting an 

 articulated palpus^ or feeler ; 4, the raando^ or lacinia, which forms the 

 inside of the maxilla, and is clothed with stiif In-istles. In the predatory 

 Coleoptera its apex is curved, and often articulated, as in « Cicmdela 

 {pi. 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 labium., or lower lip, closes the mouth below, and although it corre- 

 sponds with the upper lip, it is a much more complicated organ. In some 

 points of view it may be compared with a pair of maxilla3 united in a single 



341 



