184 



PTILOTA. 



section they are very similar in this respect, although shorter, 

 and composed of fewer joints. These organs are, however, 

 in general very short, and composed of three or fom- joints; 

 and in many groups they are entirely wanting in the larva 

 state. 



The eyes of larvae are not, like those of the perfect insect, 

 formed of an innumerable series of hexagonal lenses, but con- 

 sist of a small number of simple granvdar tubercles, placed at 

 the side of the head, in the same situation that the eyes of 

 the future insect are to be developed j they are, therefore, 

 more analogous to the simple eyelets of many insects, 

 subsequently described under the name of ocelli; many 

 larva3 are, however, entirely destitute of them. Their num- 

 bers, when present, seldom exceed six on each side, which is 

 the number possessed by the caterpillars of butterflies (fig. 20, 

 a). The larvae of the di*agon-flies have eyes somewhat re- 

 sembling those of the perfect insect. 



^^x, v\!i,^°il./. 



The mouth of the majority of larvae consists, like the mouth 

 of the perfect insect, of an upper lip (fig. 20, c), a pair of 

 horny jaws (fig. 20, d), a second or lower pair of jaws of less 

 firm consistence (fig. 21, e), furnished with an articulated pal- 

 pus (fig. 21, /), and a lower lip (fig, 21, g), furnished also 

 with a pair of articulated palpi (fig. 21, ^/i). Here, how- 

 ever, it is to be remarked, that the structure of the mouth of 



