( 293 ) XVII. The structure and life history of Psychoda sex-punctata, Curtis. By John Alexander Dell, B.Sc. Communicated by Prof. L. C. Miall, F.RS., F.E.S. [Read May 3rd, 1905.] Habitat and Mode of Life. Psychoda in all stages of growth abounds throughout the year at the Leeds Sewage Works, and advantage has been taken of this circumstance to investigate more fully the life history of the insect. It obtains its food from heaps of coke, over which crude sewage is sprayed during the purifying process. The life which flourishes on the coke-heaps, and especially the bacterial life, effects the reduction of the sewage to a harmless liquid. Alga?, among which Stigeoclonmm tcnue is conspicuous, find here congenial conditions, and supply nutriment to insects of more than one kind. Besides Psychoda, a Chironomus and a beetle (Platystclhus) occur. A Scolopendra, Mites, and Nais have also been observed on the coke-heaps. The Psychoda-\&rv& is minute, cylindrical, tapering toward the hinder end, and bluntly rounded in front. It may attain a length of 7 5 mm. The larva bears no locomotor appendages, but moves in a vermiform manner. On the fore part of the head are a pair of jaws, probably mandibles, which can be extended forwards, or folded backwards. By means of these and the recurved labium food is crammed into the mouth. The last segment is usually bent upwards so as to keep its tip, which bears the only functional spiracles, clear of the semi-liquid filth in which the rest of the body is usually immersed. The pupa? are found together with the larvae in the sewage. The fly is small and of grey colour. The female is 4 to 4*5 mm. long, the male only 2"5 to 3 mm., including the wings. The male is further distinguished by the large genital appendages, which project from the extremity of the abdomen. The wings are longer than the body, which they completely cover, and slope when at rest. Both TRANS. ENT. SOC. LOND. 1905. — PART III. ( OCT. )
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