490 EXTERNAL ANATOMY OF INSECTS. 



head, forming its sides and posterior angles, and includ- 

 ing the hinder part of the eyes, the vertex, and the occi- 

 put. They seldom exhibit any tangible character, ex- 

 cept in certain ants (Atta Latr.), in which their angle 

 terminates in one or two strong spines, giving the ani- 

 mal a most ferocious aspect; and in that remarkable ge- 

 nus Corydalis they are armed below with a tooth or point, 

 which was not overlooked by De Geer a . 



viii. Oculi b . — I must now call your attention to organs 

 of more importance and interest, and which indeed in- 

 clude a world of wonders : I mean the eyes ( Oculi) of 

 insects. These differ widely from those of vertebrate 

 animals, being incapable of motion. They may be re- 

 garded as of three descriptions — simple, conglomerate, 

 and compound. 



1. Simple Eyes c . We will consider them as to their 

 number, structure, shape, colour, magnitude, situation, and 

 arrangement. 



As to their number, they vary from two to sixteen. 

 In the flea, the louse, the harvest-man [Phalangium), 

 there are only a pair ; in the bird-louse of the goose 

 (Nirmus Anseris), and probably in others of the same 

 genus, there are four d ; in some spiders (Scytodes, Dys- 

 dera, and Segestria Latr. e ), and some scorpions f , there 

 are six. In the majority of spiders and Scolopendra mor- 



* De Geer iii. 561. t. xxvii./. 1. b Plates VI. VII. XXVI. h. 



<= Plate VII. Fig. 8, 9. XXVI. Fig. 43. h. 



d Viz. one on each side above, and one below. 



Walckenaer Araneides, t. v.f. 50, 52. t. viii./. 82. 



f Treviranus (Arachnid. 4.) says that Scorjno Europceus has only 

 two eyes. He appears to have overlooked the two on the anterior 

 side of a tubercle at each angle of the head, where they are large, 

 but not conspicuous, at least in ray specimen. 



