ANATOMY OF THE GOUT-FLY OF BARLEY. 



8ir 



to be serrate ; into it n.re inserted the dtpressor iimscles of tlie 

 mandibles. The median ventral piece bears two rather prominent 

 circular sense organ^, one on each side of its anterior region. 



Tracheal System. 



The anterior spiracles (text-fig. 22) are borne dorso-laterally 

 by tlie first thoracic segment in its posterior third and pioject 

 forwards close to the surface of the segment. Tliey are ^ery 

 prominent structures, consisting of a rather bro.ad dorso-ventrally 

 ilattened central stem, bearing about 13 lateral branches. Along 

 the median region of the central stem are a series of small 

 fissures (_/'.), which apparently pass right through the stem, being 

 only covered by the delicate membrane hy which the whole struc- 

 ture, except the apices of the branches, is covered. 



Text-fieure 22. 



IS. comhinata. Anterior spiracle. 



The posterior spiracles (text-fig. 23) are carried at the apices of 

 two pi'ominent posterior stigmatic papillae. There is no definite 

 chitinized stigmatic plate. The form of the stigmata and the 

 branching liairs may be seen from the figure. The stigmatic 

 scar {s.c), which I have failed to find in C hlor ops a-nd Aferomyza, 

 is fairly prominent in Balioptera, but it does not occupy the 

 position in A\hich it is found (as the " Button ") in most Muscid 

 larv.'e. It lies on the median side of the stigmatic papillre some 

 distance below tlie apex. 



The distribution of the tracheae is essentially similar to that in 

 Chlorops, the chief difi'erence being the branches given off" from 



