INSECTS. 69 



elevations on the sides of the head, and have a bearer-shaped 

 retina, surrounded by dark pigment, a roundish lens, and a con- 

 vex prominent cornea; and partly compound reticulated eyes 

 (oculi), that is to say, prominent (roundish, reniform, or deeply 

 notched) projections on the two sides of the head, which in the 

 males sometimes even meet upon the vertex, sometimes sit upon 

 immoveable stalks, and possess an immense number (often many 

 thousands) of facets of equal size, each of which forms, as it were, 

 the cornea of a minute eye. We also find a pyramidal lens, with 

 an obtuse apex directed towards the beaker-shaped vitreous body, 

 an optic nerve dilated like a horn, and a dark pigment, as to the 

 co-operation of which in the formation of an image we can form no 

 idea. In some insects we find both simple and compound eyes. Then 

 two or three ocelli are seated above upon the vertex, and so near 

 to the cephalic ganglion that their optic nerves only form short 

 warts. The function of the ocelli is unknown ; but they do not 

 appear to be organs of distant sight, as some will have it, as their 

 cornea and lens are always very convex. 



The oral organs follow a single fundamental type of structure, 

 and are sometimes adapted for suction and sometimes for biting. 

 The manducatory organs consist of 1, a median upper lip (labrum 

 = Oberlippe = Lefze) ; 2 of two lateral, generally hook-shaped, 

 horny mandibles (mandibulae = Oberkiefern = Kinnbacken) ; 3, of 

 two other lateral jaws (maxilla = Unterkiefern = Kinnaladen) 

 placed beneath these, usually furnished with jointed appendages, 

 the so-called maxillary palpi (= palpi maxillares) ; 4, of a lower lip 

 (labium = Lippe) placed quite beneath, which is also provided 

 with palpi, the so-called labial palpi (palpi labiales = Lippen- 

 tastern), and like the labrum is capable of moving up and down. 

 The upper lip, which is rarely immoveable, generally moveably 

 articulated to the lower surface of the head, covers the mandi- 

 bles from above. The mandibles consist of two hollow, horny 

 pieces, which are attached by a hinge on each side of the head, 

 and can only move in opposition to each other. The less solid 

 nourishment the animal takes, the more insignificant do the 

 mandibles become, and at last they are entirely wanting in the 

 suctorial insects. The maxilla are very composite, weaker and 

 less toothed than the mandibles ; they approach very close to the 

 labium, or are even coalescent with it, and consist of a shaft or 

 stalk (stipes), which is composed of a transverse angle (car do), 

 and the true stalk (stipes), which is often hook-like, hard, and 



