BY T. HARVEY JOHNSTON AND M. J. BAXCEOrT 



05 



We have found the following ratio (expressed as a per- 

 tcentage) to be a useful and ready means for identifying 

 the larvae of the three species, viz., the ratio which the 

 distance from the mouth to the base of the oesophagus 

 bears to the total bod}' length. The average percentages 

 .are about 37 in the case of //. muscce, 28 for H. megastoma, 

 and 42 (38-44) for H. microstoma (based on Hill's figures). 



Previous observers do not apj)ear to have noted the 

 presence of well-marked annulations on the anterior region 

 of many fully - developed larvae of H. megastoma, 

 H. muscce, and H. microstoma. 



MuscA DOMESTiCA cis au intermediary of H. muscje and 



H. MEGASTOMA, 



Examination of cajitured flies. 

 Flies were captured on several occasions in Eidsvold 

 in stables where race-horses were kept. Onl\- the one 

 species, J/, domeslica, was represented in the collection 

 from this situation. Of 122 flies so caught, 10 were found 

 to be infected with Hahronema ; in one case no record of 

 species was kept ; H. muscce occurred alone 8 times ; 

 while H. muscce and H. megastoma were j)resent together 

 once. Of 8 flies captured away from stables none were 

 infected. Both sexes were present in the jDarasitised 

 material. 



