THE FLY. 33 



or brain, and the nerves of sense proceeding there- 

 from to the organs just named. 



2. The thorax, or chest, is again subdivided into 

 three parts ; — ^imperfect rings, the anterior of which 

 is termed the prothorax, the middle the mesothorax, 

 and the posterior the metathorax. On these three 

 rings the members of locomotion are distributed as 

 follows : viz. on the prothorax is found the first pair 

 of legs only ; on the middle or mesothorax, which in 

 the Fly is largely developed, the second pair of legs 

 and the pair of wings (for, as before remarked, the 

 Ply possesses but owe pair) ; and on the metathorax 

 the last pair of legs, and two organs, termed the 

 halter es or poisers -j—^he last-named will be folly 

 described hereafter. Within the thorax is situated 

 the continuation of the nervous system (which here 

 consists of the nervous chord, the thoracic ganglion 

 and nerves branching from it to the members; see 

 PI. I. fig. 1) ; also the stomach and part of the circu- 

 lating and respiratory apparatus. 



3. The abdomen, which bears no external mem- 

 bers, is also composed of several rings, and contains 

 the intestinal canal, with its appendages ; two pul- 

 monary sacs, with other portions of the respiratory 

 apparatus ; the many-chambered heart, and the re- 

 productive organs. 



Having thus glanced in a cursory manner at the 

 form and structure of the Fly, we shall in our next 

 enter into a more particular account of its various 

 organs. 



c 5 



