8 THE ORGANS OF INSECTS 



three main parts the head, the thorax, and 



The Head, the abdomen. The head is furnished with 

 eyes, antenna, the mouth-parts, and in certain 

 species, organs supposed to diffuse scent, or 

 to be capable of guiding the male to the female. 



TheXn. The antenna are regarded as sense-organs, 

 discharging olfactory and even auditory func- 

 tions by means of particular parts. They are 

 composed of numerous joints, and are inserted 

 between or in front of the eyes. 



The Mouth- The mouth-parts of insects are somewhat 

 complicated. In the Orders with which we are 

 here concerned, they consist of a labrum or 

 upper lip, a pair of mandibles or biting jaws, 

 which in the adult members of the EPHEMERIDVE 

 and TRICHOPTERA 1 are much modified and even 

 atrophied, a second pair of jaws, termed max- 

 illa, and then the labium or lower lip, which is 

 really made up of a second pair of maxilla 

 welded to the labium. 



The Palpi. Attached to the maxilla are their palpi, which 

 are jointed processes, and organs of touch. 

 Thus there are usually four of these pro- 

 cesses 2 two attached to the first pair of maxilla 

 and termed maxillary palpi, and two attached 

 to the second pair of maxilla, or the labium, and 

 called labial palpi. These palpi are of great 



1 Certain species of the TRICHOPTERA are apparently able 

 to partake of fluid or soft food by suction in the absence of 

 serviceable mandibles. When dissecting specimens for micro- 

 scope preparations, I have frequently found food in the ali- 

 mentary canal in quite appreciable quantities. 



2 In certain genera of the TRICHOPTERA the palpi are atro- 

 phied, or completely absent. 



