THE CLASS or INSECTS. 



ramify throughout the whole interior of the animal, and con- 

 n?ct with breathing pores (stigmata) in the sides of the body. 

 They do not breathe tln-ougli the mouth as do the higher ani- 

 mals. The trachcEe and blood-vessels follow closely the same 



Fig. 4. 



course, so that the aeration of the blood goes on, apparently, 

 over the whole interior of the body, not being confined to a 

 single region, as in the lungs of the vertebrate animals. 



Thus it is by observing the general form of the body-walls, 

 and the situation of tlie different anatomical systems, both in 

 relation to themselves and the walls of the body, or crust, 

 which surrounds and protects the more delicate organs Avit'.iin, 

 that we are able to find satisfactory characters for isolating, in 

 our definitious, the Artliropoda from all other animals. 



We shall peiceive more clearly the differences between tlie 

 two branches of articulated or jointed animals, namely, the 

 Worms and tlie Arthropoda, by examining their yonng 



often as lungs. The nervous cord (,n) rests on the floor of the cj'hnder, sending a 

 filament into the oar-like feet (/), and also around the intestine or stomach (t), to a 

 supi)lcmentary cord {d), which is situated just over the intestine, and under th3 

 heart or dorsal vessel (c). The circle c and e is a diagram of the circulatory sys- 

 tem; c is the dorsal vessel, or heart, from the side of which, in each ring, a small 

 vessel is sent downwards and around to e, the ventral vessel. — Orir/innl. 



Fig. 4. An ideal section of a Bee. Here the crust is dense and thick, to which 

 strong muscles arc attached. On the upper side of the ring tlic wings grow out, 

 while the legs are inserted near the under side. The tracheaa (d) enter through the 

 stir/ma, or breathing i)ore, situated just under the wing, and their branches sul)- 

 divideand are distributed to the wings, with their live piiucipal veins as indicated 



