DIPTERA 827 



pair of conical, leg-like appendages. On the ventral side of the body 

 (Fig. 1052, b) each of the seven larger segments except the last bears 

 a sucker, the cavity of which extends far into the body, and each of 

 these segments except the first bears two tufts of tracheal gills ; but 

 those of the last segment are united. The head, which forms the 

 front end of the first of the seven larger divisions, bears a pair of 

 slender antennae, each of these consists of a very short basal segment 

 and two long segments; at the tip of the last of these there is a pair 

 of minute appendages and a bristle. The suture between the head 

 and the remaining parts of the first division is best seen on the ventral 

 side of the body. On the dorsal side a suture may be seen dividing 

 the last division into two segments. 



The pupa-stage is passed in the same place as the larval. Like 

 the larvae the pupae are very conspicuous on account of their black 

 color, and are apt to occur like the larv« closely clustered together. 

 The pupa is not enclosed in the larval skin, and differs greatly in form 

 from the larva. On the dorsal side the skin is hard, forming a convex 

 scale over the body (Fig. 1052, c); and the thorax bears a pair of 

 breathing organs, each composed of four flattened leaves, two of 

 them delicate tracheal gills, and the other two protecting chitinized 

 plates; on the ventral side the skin is very delicate, soft, and trans- 

 parent; so that the developing legs and wings may be easily seen 

 when the insect is removed from the rock. The pupae cling to the 

 rock by means of six suckers, three on each side near the edge of the 

 lower surface of the abdomen ; and so firmly do they cling that it is 

 difficult to remove specimens without breaking them. 



I have watched the midges emerge from their pupa-skins and 

 escape from the water. The pupae occurred in groups so as to form 

 black patches on the rocks. Each one was resting with its head down 

 stream. Each midge on emerging forced its way out through a trans- 

 verse rent between the thorax and abdomen. It then worked its 

 body out slowly and in spite of the swift current held it vertical. The 

 water covering the patch of pupae varied from 6 mm. to 25 mm. in 

 depth. In the shallower parts the adult had no trouble in working 

 its way to the surface still clinging to the pupa-skin by its very long 

 hind legs. 



While still anchored by its legs the midge rests on the surface of 

 the water for one or two seconds and unfolds its wings; then freeing 

 its legs it takes flight. The adults emerging from the deeper water 

 were swept away by the current before they had a chance to take 

 wing. The time required for a midge to work its way out of the pupa- 

 skin and take flight varied from three to five minutes. 



The larvae of the net-winged midges live only in swift-flowing 

 streams; they are found, therefore, only in mountainous or at least 

 hilly regions. It is believed that they feed chiefly on algae and di- 

 atoms. It does not seem probable that these delicate midges can 

 deposit their eggs on the rocks in the swift-running water where the 

 larvae live, as do the females of Simulium. It is more likely that the 

 eggs are deposited on the wet rocks at the margins of the stream and 

 that the larv^ migrate to the center of the stream. 



