THE CLASS OF INSECTS. 



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

 nect with breathing pores (stigmata) in the sides of the body. 

 They do not breathe through the mouth as do the higher ani- 

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



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 the different anatomical systems, both in 

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

 which surrounds and protects the more delicate organs within, 

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

 our definitions, the Arthropoda from all other animals. 



We shall perceive more clearly the diftereiiecs between the 

 two branches of articulated or jointed animals, namely, the 

 ^Vorins and the Arthropoda^ by examining their young 



often as hiiif^.s. The norvons cord («) rests on the floor of the cylinder, sending a 

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

 suiii>lementar_v cord ((/), which is situated just over the intestine, and under the 

 heart or dorsal vessel (c). Tlie 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 snuiU 

 vessel is sent downwards and around to c, the ventral vessel.— OrUjinal. 



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

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

 while the legs are inserted near the under side. The trachere {d) enter through the 

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

 divide and are distributed to the wuigs, with their iive principal veins as indicated 



