96 ON THE ANATOMY OF THE PLY. 



Section XVIII. The Halteres and Wing Organs. 

 PLATE VIII., FIGS. 3 TO 7. 



The halteres are evidently modifications of the posterior 

 wings. The halter consists of three portions : the base, which 

 is covered with numerous special organs arranged in rows, 

 the pedicle, and the globe. 



The base is connected with the thoracic integument. Three 

 hardened folds surround it, and have several slender muscles 

 inserted into them. These move the whole organ, which is 

 very movable. 



The special organs at its base are arranged in four sets, two 

 on the upper and two on the under surface. Each set consists 

 of a series of curved ridges, under which these organs are 

 placed. Three of the sets are represented in Plate VIII., 

 fig. 3. The fourth is similar to the lower set, and is placed 

 opposite to it. 



The proximal sets form segments of a hemisphere, and the 

 distal ones are arranged on two half-cylinders. 



On making a section of the base, there appears to be but 

 one cavity. If the two half-cylinders are completed internally, 

 it is only by a thin membrane ; but as each seems to open 

 into the pedicle of the halter by a separate opening, I think 

 this is extremely probable. The ridges under which the 

 special organs are arranged are convex transversely, and each 

 of the grooves between them bears a single row of curved 

 hairs. These are close and long in the proximal sets, but 

 short, strongly curved, and distant in the distal groups. 



