ANATOMY OF TUE GOUT-FLY OF BARLEY. 



811 



ronglily triangular plate bearing four small circular seiise organs, 

 a larger central one and an anterior and two posterior smaller 

 ones. The labial plate bearing the two labial sense organs 

 occupies the same position as in Chlorops, but difiers somewhat 

 in shape. The position of the small circular cephalic sense 

 organs is shown in text-fig. 15. At each side of the oral aper- 

 ture, running more or less paiallel to its lateral margin, there 

 are three cliitinons i-idges Avhicli extend from the autero-lateral 

 region of the mouth-opening to its postero-lateral region. 



Thoracic Segments. 



Instead of rows of chitinous teeth such as occur on Chlorops, 

 Meromyza has low transverse ridges of varying lengths, the 

 apices of the ridges being minutely serrated. Almost the whole 

 of the dorsal surface of the prothoracic segment bears these ridges, 

 only a narrow ]iosterior region being free from them. Ventrally 

 the ridges extend across the whole breadth of the anterior 

 margin, but passing posteriorly they become less and less exten- 

 sive, so that they form a roughly triangular area, the base of the 

 triangle lying across the anterior margin of the segment, the 

 apex of the triangle lying in the median region of the segment a 

 little anterior to its posterior margin. 



The meso- and metathoracic segments hsive ridges all round 

 their anterior borders, the ridges loeing numerous, closely placed, 

 and covering broad areas in the middle of dorsal and ventral 

 surfaces, but becoming much less numerous, wider apart, and 

 confined to a narrower area laterally. 



In the antero-ventral region of each thoracic segment is a 

 ti-ansverse series of circular sense organs, five on each side of the 

 median line. The vestigial rudiments of the legs are similar to 

 those of Chlorops. 



Abdominal Segments. 



There are nine abdoujinal segments, the ninth being rather 

 small with its posterior region capable of partial withdrawal into 

 its anterior. The anus, which is situated ventrally on the 

 a.nterior region of the ninth abdominal segment, is a narrow, 

 longitudinal slit, bounded on each side by a fairly prominent oval 

 swelling; there are no adjacent chitinous teeth or special sense 

 organs." The last abdominal segment is divided posteriorly into 

 -two lobes by a deep and broad vertical fissure; the sessile 

 posterior stigmata lie facing one another, one on each side of the 

 fissure. 



Chitinous ridges, similar to those on the thoracic segments, 

 surround the anteiior regions of each abdoininal segment except 

 the last. No ridges occur rouiul the posterior border of any 

 segment. There are no ambulatory swellings. 



Circular sense organs, similar to those on the thoracic segments, 

 occur in tiansverse rows of about ten on the ventral surface lu 



