14 NORTH AMEUICAN DIPTERA. 



vein wanting ; the third vein arises from the first usually at 

 such an angle that its first section (to the anterior oross-vein) 

 has the appearance of a cross-vein ; fourth vein always, the 

 third and fifth either furcate or not ; sixth vein never furcate, 

 sometimes rudimentary ; seventh vein usually short, often 

 rudimentary or entirely wanting ; discal and posterior basal 

 cells always wanting. 



The family Mycetophilida', commonly known as fungus- 

 gnats, comprises seven or eight hundred known species of 

 small or minute flies, the best known of which are, perhaps, 

 the various dark-winged species of Sclara so common about 

 gardens. In the following description of the immature stages 

 1 draw largely from Osten Sacken. 



The larva? have a distinct horny head ; horny, flat, lanielli- 

 form mandibles ; maxilhe with a large coriaceous inner lobe 

 and a horny outside piece, with a circular excision at the tip, 

 the labium small, horny, almost rudimentary ; the antenme 

 are usually small or rudimentary, the ocelli are either wanting 

 or seen in a small pellucid spot below each antennae. The 

 body is siibcylindrical, more or less elongated, fleshy, whitish 

 or yellowish, and composed of twelve segments. It is smooth, 

 without hairs or bristles, except those on the ventral side. It 

 is generally transi)arent, showing distinctly the intestinal 

 canal and the trachea. There are eight pairs of stigmata, one 

 on the first segment, and seven on the first seven abdominal 

 segments, the last two having none. The locomotory organs 

 consist of more or less ai)parent transverse swellings on the 

 under side of the ventral segments, sometimes furnished with 

 miimte bristles or spines. 



The larva? present some of the most singular habits among 

 all di})tera. They are gregarious, and live in or upon decaying 

 matter. Most of the species seem to jn-efer fungus or fungoid 

 substances, wlience comes the conunon name of fungus-gnats 

 apjjlied to tlie mature insect. The larva? of Sclara are found 

 among decaying leaves, in vegetable mold, in cow-dung, under 



