IV 



INTRODUCTOKY. 



The abdomen contains the ovipositor; sometimes, as in the 

 bees and wasps, forming a sting. In the spiders (Fig. 1), 



however, there are no an- 

 teunfe, and the second 

 maxillas, or labium, is 

 wanting. Moreover, there 

 are four pairs of legs. 

 The centipedes (Fig. 2, a 

 Myriopod) also differ from 

 >s the rest of the insects 

 in having an indefinite 

 number of abdominal 

 I'ings, each bearing a pair 

 of legs. 



On examining the ar- 

 rangement of the parts 



1. Spider (Tegenaria). 



Within, we find the nervous cord, consisting of two chains of 

 swellings, or nerve-knots, resting upon the 

 floor or under side of the body ; and the heart, 

 or dorsal vessel, situated just under the skin 

 of the back; and in looking at living cater- 

 pillars, such as the cut- worm, and many thin- 

 skinned aquatic larvaj, we can see this long 

 tubular heart pulsating about as often as our 

 own heart, and when the insect is held against 

 its will, or is agitated, the rapidity of the pulsa- 

 tions increases just as with us. 



Insects do not breathe as in the higher ani- 

 mals by taking the air into the mouth and filling 

 the lungs, but there are a series of holes or 

 pores along the side of the body, as seen in the 

 grub of the humble bee, through which the air 

 enters and is conveyed to every part of the body by an immense 

 number of air tubes. (Fig. 3, air tubes, or trachete, in the cau- 



Ceutipede. 



