428 



THE STUDY OF INSECTS. 



opening, which is formed by a lengthwise split on the back 

 near the head-end and a crosswise split at the front end of 



this (Fig. 498). In a few members 

 of this suborder (i.e., some of the 

 Cecidomyiidae) the pupa escapes 

 FlG - * 98 - through a crosswise split between 



the seventh and eighth abdominal segments. The pupae 

 are usually either naked or enclosed in the last larval skin, 

 the puparium ; but the pupae of some of the gall-gnats, 

 Cecidomyiidae, are enclosed in cocoons. The adult flies do 

 not possess a frontal lunule. See footnote page 416. 



Family PsYCHODlDiE (Psy-chod'i-dae). 

 The Moth-like Flies. 



There may be found frequently upon windows and on 

 the lower surface of the foliage of trees small flies which 

 have the body and wings densely clothed with 

 hair and which resemble tiny moths in appear- 

 ance. The wings are broad, and when at rest 

 slope at the sides in a roof-like manner or are 

 held horizontally in such a way as to give the FlG _ A 

 insect a triangular outline (Fig. 499). moth-iike fly. 



The moth-like appearance of these insects is sufficient to 

 distinguish them from all other flies. The venation of the 



vn» 



Pig. 500.— Wing of a moth-like fly. 



