INSECT A. 227 



without wings, that always preserve their natal form, and 

 merely increase in size and change their skin(l). In this re- 

 spect they bear some analogy to the animals of the preceding 

 classes. Nearly all the remaining Hexapoda have wings; but 

 these organs, and even frequently the feet, do not make their 

 appearance at first, but are only developed after a series of 

 changes, more or less remarkable, styled metamorphoses, of 

 which we shall soon have to speak. 



The head(2) bears the antennse, eyes, and mouth. The 

 composition and form of the antennae are much more various 

 than in the Crustacea, and are frequently more developed or 

 longer in the males than in the females. 



The eyes are either compound or simple ; the first, accord- 

 ing to the baron Cuvier, Marcel de Serres and others, are 

 formed: 1, of a cornea, divided into numerous little facets, 

 which is so much the more convex, as the insect is more car- 

 nivorous ; its internal surface is covered with an opaque, and 

 variously coloured, but slightly fluid substance, usually, how- 

 ever, of a black or deep violet hue ; 2, of a choroides, fixed 

 by its contour and edges to the cornea, covered with a black 

 varnish, exhibiting numerous air vessels, arising from tolera- 

 bly large trunks of tracheae in the head, whose branches form 

 a circular trachea round the eye : it is frequently wanting, 

 however, as well as the choroides, in various nocturnal in- 

 sects; 3, of nerves arising from a large trunk, proceeding di- 

 rectly from the brain, which then opens, forming a reversed 

 cone, the base of which is next to the eye, and each of whose 

 rays or threads traversing the choroides and lining matter of 

 the cornea, terminates in one of its facets ; there is no crystal- 

 line nor vitreous humour. 



Several, besides these compound eyes, have simple ones, 

 the cornea of which is smooth. They are usually three in 



(1) My Homotenes (similar to the end) or the Ametobolia of Leach. 



(2) Its surface is divided into several little regions or arese called the cli/peus 

 (nose of Kirby), the fare, the front, the vertex or summit) and the cheeks. The 

 term clypeus being equivocal, I have substituted for it that of epistoma or over 

 mouth, it g-ives insertion to the labrum or upper lip. 



