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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. ) 



