426 



STUDIES IN LIFE-IIISTORIES OE AUSTRALIAN DIPTKRA BRACIIYCERA, 



Tlie ,Straliumf/iiilae beliing to that group of fly larvae oharaeterist'd by 

 having parallel jaws, woiking upwards, or outwards, and downwards, jis dis- 

 tinguished from those with opposing, horizontally moving mandibles. The adap- 

 tation accords with thci^ method of obtaining nourishment by suction, instead 

 of by biting and chewing; and the larval Metopunia riibriceps. which lives on 

 the juices in the roots of grasses, shows this feature very well. A liricf des- 

 cription of the mouth-parts is contained in the first paper of this series (Irwin- 

 Smith, 1920). The present paper gives the results of more detailed morpholo- 

 gical investigations. 



Mouth-parts. 



Hounding the upper side of the oral aperture is a smooth, cylindrical, peg- 

 like process, the median process (hi.;).). It is not movable, and is really the 

 terminal apex of the shield-shaped sclerite which covers the greater part of the 

 dorsal surface of the head (Text-fig. 2). At the base of the median process 

 the lateral edges of the sclerite bend inward and downward into the interior 

 of the head, forming a sort of internal skeleton, and enclosing a cavity which 

 continues up into the median process (Text-fig. .3). The process appears to 

 be a composite structure, formed by the fusion of a median and two side pieces. 

 On the ventral side, where the fusion is incomplete, two longitudinal slit-like 

 apertures communicate with the hollow interior of the process. Laterad of those 

 are two downwardly directed knoli-like projections. On the dorsal surface, 

 the anterior extremity of each side piece is marked by a ridge, and immediately 

 in front of this is inserted a fine hair (Text-fig. 1). A similar, but somewhat 

 larger hair is situated further hack, in a deep circular depression. The median 

 jH-ocess measures about 0.03 mm. across the tip, and 0.14 mm. from tip to base 

 on ventral side. Tlie whole sclerite, including the median process, and the in- 

 ternal ridges, is composed of very dense, dark brown chitin. and <'an be dis- 



Text-figures 1-6. 



I. Dorsal view of anterior end of head, (x 120). 2. E.xternal view of dorsal sclerite. (x 32). 



;!. Internal view of tlie same, with one lateral plate still attacheil. (xf>6). 4. Ventral 



view of mouth parts, (x 120). 5. Mouth jaws, (x IflfJ). 6. Portion of cuticuhir wall 



just below ventral processes showinfj (jlandular apertures (.'). (x 320). 



/, jaw ; /./>., lateral plate ; w.^., median process. 



sected away from the remaining parts of the head in a single piece (Text-fig. 2). 

 Posteriorly, it is connected up with the sides of the head by a stout, mem- 

 branous cuticle, having an armour of hexagonal plates somewhat similar to those 

 on the body (Text-fig. 3). Furtlicr up, it is firmly fused with the dense chitin 

 which forms the lateral "bosses" and extends forward in the shape of two 



