50 G. F. HILL. 



uninterrupted fringe of long and short bristles arranged roughly in two rows, the 

 shorter bristles nearer the base ; on each segment from the 2nd to 5th these bristles 

 increase in length ; on the 5th, 6th and 7th they are equally long or, rarely, the long 

 bristles may be absent from the middle of the seventh tergite and sternite and the 

 shorter ones may be branched. 



The six projecting spurs at the apex of the abdomen are arranged three on each lobe 

 of a prominent bilobed tubercle divided vertically by a deep cleft, which is wider in the 

 males ; the upper and middle pair are equally long and stout, the lower are smaller ; 

 on either side of the dorsal surface midway between the base of the tubercle and the 

 apex of the 7th segment there is a group of four or five stout spines of unequal length. 

 The length and stoutness of these bristles vary greatly in individuals of either sex. 



The anal tubercle is very large and deeply furrowed in the male and is bordered 

 anteriorly by an unbroken fringe of about 18 to 22 stout bristles of variable lengths. 

 In the female the fringe is broadly interrupted in the middle, and consists of from 6-9 

 bristles on either side (fig. 8). 



Fig. 8. T. aprepes, ventral surface of last segment of female pupa. 



Duration of the Pupal Stage. The duration of the pupal period during the months 

 June-September varied from 8 to 20 days, the average being 12 days in the case of 

 10 individuals whose p^iods were accurately observed. 



The factors which determine early or late emergence of laboratory specimens are 

 not known, and no explanation can be offered at present of the fact that whilst certain 

 pupae of a batch pass through a very short pupal stage — e.g., eight days — others of 

 the same batch and subjected to the same treatment may remain in 'the stage for 

 periods up to 20 days. 



Emergence of the Fly. The emergence of laboratory-bred flies has been observed 

 on several occasions — always between 10 a.m. and 4.30 p.m. — and in each the pro- 

 cedure was similar. The pupa, with its body vertical, works its wav to the surface, 

 from which it protrudes the thorax and first two or three abdominal segments. In 

 this position it remains motionless for from one to two hours ; then, with very little 

 apparent effort, the thorax is burst on the dorsal surface to the posterior margin of 

 the mesothorax, and also along the lower margin of the eyes, leaving a flap-like piece 

 bearing the anterior group of tubercles more or less loosely attached ventrally. The 

 fly frees itself in a minute or two, leaving the greater part of the pupal case as before. 

 At emergence the wings are uniformly opaque, but in the course of an hour or two 

 they become hyaline or suffused with brown, as the case may be. 



The Adult. The adults of this species show considerable variation in regard to 

 size and coloration and, as might be expected, in laboratory-bred specimens this is more 



