66 ON THB ANATOMY OP THB FLY. 



nervures arise in a fold of the wing posterior to the sub- costal 

 nervure, which all become very fine, and are ultimately lost 

 'near the posterior edge of the wing, which is not guarded by 

 any nervure. These are not connected with the cavity of 

 the thorax by any open canal, like the costal and sub-costal 

 nervures ; but the two systems communicate by a short trans- 

 verse trunk from the posterior branch of the sub-costal near 

 the middle of the wing. 



. The costal nervure is protected at its origin by a small scale or epaulet 

 called the pterogodium, fringed with hairs ; beneath this is a broad scale- 

 like fold, which forms the basal joint of the costal nervure, and which is 



DESCRIPTION OF PLATS VI. 

 The Development and Appendages of the Thorax, 



Fig. 1. The nerve centres of the larva, with the imaginal discs of the 

 optic and antennal segment-, and of the four anterior legs firmly attached 

 to them, x 30 diam. 



Fig. 2. The lateral tracheal vessel of the larva, showing its inner and 

 outer coat, "with the imaginal discs of the wing, halter, and posterior leg 

 firmly attached to it. x 30 diam. 



Fig. 3. The first stage of unfolding of the imaginal discs of the ante- 

 rior pair of legs, showing their capsules, x 15 diam. 



Fig. 4. One of the anterior leg discs unfolded and considerably de- 

 veloped ; about the third day of the pupa state. X 30 diam. 



Fig. 5. The same, at the end of the first week, with the leg of the fly 

 seen within in process of development, x 20 diam. 



Fig. 6. The intermediate leg of the fly. x 10 diam. 



Fig. 7. The tibia of the same, with muscles attached, x 10 diam. 



Fig. 8. The first tarsal joint, with its muscles, x 10 diam 



Fig. 9. The last three tarsal joints, x 20 diam. 



Fig. 10. The last tarsal joint, with its long apodeme and muscle, 

 arising from the femur. X 10 diam. 



Fig. 11. The pulvilli and claws, x 75 diam. 



