ANATOMY OP TUE GOUT- FLY OF BARLEY. 803 



The mesotliovacic leg discs lie slightly posterior and ventral to 

 the profchoraeic discs; their peduncles pass forwards to the 

 ventral hypodertn of the mesothoracic segment. In the speci- 

 mens studied the mesothoracic iinaginal leg sacs did not 

 communicate with one another, though they probably do so at a 

 later stnge. 



The mebathoracic leg discs are posterior to the mesothoracic 

 and rather more lateral and dorsal. They are united to both 

 the wing and haltere discs by strands of tissue accompanied by 

 small trachere derived from the third lateral tracheal trunk. 

 The figure given by Lowne (p. 84) of the v/ing, haltere, and meta- 

 thoracic leg discs of the larva of CcdUphora approximates very 

 closely to the condibion found in Cklorops. 



In a fairly mature lM,rva a small imaginal disc can be found 

 arising just posterior to the anterior stigmatic trunk on each side 

 at the point where this traverses the hypoderui. Iti the most 

 advanced stage so far examined these discs are only shallow 

 invaginations of imaginal cells and cannot be said to consist of 

 peripodal cavity, peripodal membrane, and imaginal disc. They 

 may, however, and probably do, increase in complexity towards 

 the end of larval life. 



The wing rudiments are the largest of all the imaginal discs; 

 they lie mainly in the mesothoracic segment, but their posterior 

 rounded ends extend into the anterior region of the metathorax. 

 Each lies mainly dorsal and internal to the dorso-ln.teral tracheal 

 trunk of its side, but anteriorly it narrows and passes dorsally 

 over the trunk to the external side of the latter. Its narrow 

 anterior end is produced into a short peduncle which passes to 

 the dorso-lataral hypoderin in the posterior region of the meso- 

 thoi-ax. 



The haltere disc lies ventral and external to the dorso-lateral 

 tracheal trunk, the bulb of the disc overlying the base of the 

 third lateral tracheal branch. Its peduncle joins the hypoderm 

 in the mid-lateral region of the metathorax. 



The innervation of the spiracular, wing and haltere discs has 

 nob been followed out. 



A minute trachea accompanies the peduncles of alF the thoracic 

 imaginal discs. 



Imaginal Discs 0/ the Mouth Parts. 



There are two pairs of imaginal mouth rudiments. The larger 

 pair, the maxillary discs, lie one on either side of the anterior 

 region of the pharyngeal mass. They are broad posteriorly, but 

 taper off anteriorly into peduncles Avhich are attached to tlie head 

 capsule just latero-dorsal to the mouth-opening. Posteriorly 

 they appear to be united dorsally to the hypoderm overlying the 

 pharynx, which is continuous posberiorly with the cephalo- 

 pharyngeal band. They are united ventrally by a hypodermal 

 sheet passing below the pharynx; 



