53 Orthorrhapha brachycera. 



in the male than in the female; it is mainly tlie third joint which 

 varies in length both in tiie various species, and in the two sexes, 

 and it may also be of another shape in the male than in the female; 

 the first joint is longer than broad, increasing in breadth from the 

 base towards the apex and thus obconical; the second joint is short 

 and likewise obconical, its apical margin is not straight, but is on 

 the inside prolonged a little triangularly in the middle, and likewise 

 on the outside above; the third joint is more or less triangular, ovate 

 or lancet-shaped according to its length, and often its point is lying 

 dorsally or turned upwards; when dissociated from the second joint, 

 it is seen to be incised in the base, and thus in reality somewhat 

 cordate in shape; the incision is different on the two sides in accord- 

 ance with the shape of the second joint. From the anterior end of 



Fig. 18 D. plumipes cJ", second and third joints of antenna, dissociated to show 

 the exact shape; a. the collar-shaped prolongation. X 100. 



the second joint issues a somewhat collar-shaped, slightly conical, and 

 a little chitinised prolongation, forming a sort of connecting membrane 

 and fitting into a similar cavity in the third joint; it is only seen, 

 when the joints are dissociated; the real connection between the 

 second and third joint lies at the end of the prolongation, which is 

 connected to the anterior end of the cavity in the third joint. The 

 two basal joints are a little compressed, the third is more compressed, 

 and strongly so towards the apex; the two last joints form an arista, 

 which is generally longer than, sometimes only as long as the antennæ 

 (the three first joints); the first joint of the arista is somewhat long. 

 The arista is inserted dorsally on the third joint, in the middle or 

 nearer the base or apex; it is inserted on a small peduncle on the 

 dorsal margin. The basal antennal joint has hairs above and at the 

 apex, the second joint has small bristles along the apical margin, 

 longest above and below; the third joint is very short-haired, some- 

 times a little more distinctly, and the arista is short- or almost micro- 

 scopically hairy. In a foreign species (the American D. hastatus) the 



