576 Dr. D. Keilin on the 



The dimensions (in centimetres) of the specimens are 



Height of anterior lobe of ilium 7*0 



Height of the proximal end 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 tlie middle of the shaft of the femur 3'6 



Width of the anterior face of vertebral centrum 4'0 



HeiLiht of tlie anterior face of vertebral centrum 4'0 



LVII. — On the Life-history of Dasyhelea obscnra, Winner tz 

 {Dijjtera^ Nemutocera, Ceratopogonidie), ivith some 

 Remarks on the Parasites and Hereditary Bacterian 

 Symbiont of this Midge. 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 ohscura 576 



n. J'^ggs and Ovipositiou 577 



III. Larva ■ 578 



(rt) Head ; (h) Thorax; (c) Abdomen; ((/) Internal Organs. 



IV. Pupa 682 



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



Authors 583 



VI. Predaceous Dipterous Larvae living, upon the Larvse and 



Pup?e of Dasi/helea obsciira 587 



VII. Parasites of Dasi/helea Larva) 587 



VIII. Hereditary Bacterian Symbiont of Dasyhelea obscura 588 



IX. References 588 



X. Explanation of the Plates , 589 



I. Habitat of the Larva of JJasykelea obscvra. 



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 stndy was obtained from a 

 wound of an elm tree standing on the Caius College ground 

 at Newuham (Cambridge) and facing Church Kate Walk. 

 In addition to Dasyhelea larvse, the decomposed sap of this 

 wound contained the larvae and pupa3 of several other 

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



