576 Dr. D. Keiliu on the 



The dimensions (in centimetres) of the specimens are 



Height of anterior lobe of ilium 7-0 



Height of the proximal eud of the pubis '. 6-0 



Width of the proximal end of the pubis (from within 



outwards) 27 



Greatest width of the acetabular cavity (from within 



outwards) 3-7 



Length of the femur, so far as preserved 31-5 



Diameter of the middle of the sliaft of the femur 3-6 



Width of the anterior face of vertebral centrum 4*0 



Height of tlie anterior face of vertebral centrum 4-0 



LVII. — On the Life-history of Dasyhelea obscura, Winnertz 

 (Diptera, Nematocera, Ceratopogonidje), ivith some 

 Remarks on the Parasites and Hereditary Bacterian 

 Symbiont of this Midye. By D. Keilin, Sc.D., Beit 

 Memorial Research Fellow (Quick Laboratory, University 

 of Cambridge). 



[Plates XIX. & XX.] 



Contents. 



Page 



I. Habitat of the Larva of Dasyhelea obscwa 576 



IL J'-^ggs and Oviposition 577 



III. Larva 578 



(a) Head; (5) Thorax; (c) Abdouit-n ; (c/j Internal Organs. 



IV. Pupa 682 



V. Larvfe of other Species of Dasyhelea, recorded by various 



Authors 583 



VI. Predaceous Dipterous Larvae living upon the Larva) and 



Pupae of Dasyhelea obscwa 587 



VII. Parasites of Dasyhelea Larvaj 587 



VIII. Hereditary Bacterian Symbiont oi Dasyhelea obscura 588 



IX. References 588 



X. Explanation of the Plates 589 



I. Habitat or the Larva of Dastselea obscusa. 



Dasyhelea obscura, Winnertz, is a very common midge, the 

 early stages of which are almost always found in the decom- 

 posed sap filling the wounds of elm trees. The material 

 which was used for the present study was obtained from a 

 w'ound of an elm tree standing on the Caius College ground 

 at Newnham (Cambridge) and facing Churcli Rate "Walk, 

 lu addition to Dasyhelea larvie, the decomposed sap of this 

 wound contained the larvse and pupa3 of several other 

 Diptera : (1) Rhyphus fenestralis. Scop., (2) Mycetubia 



