68 life history of habronema. 



Native flies as intermediate Hosts. 



I. — M. FERGUSON! Jnstn. and Bancr. 



Captured flies (Eidsvold). 

 These flies were usually captured right away from 



• stables or yards, and usually near ground where cattle 

 had been camping. (Jut of 1,176 specimens dissected 



: 26 were found to be infected with Habronema, i.e., 2.2 

 per cent. In 11 cases the worms were too small to be 

 specifically identified, and in eight cases no record of the 

 species was made. In the remaining seven cases, 

 H. megastoma occurred alone four times ; H. muscce alone 

 twice, while both species were present in one fly. Where 



• count was made of the number of worms present, it ranged 

 from one to 18, with an average of four. This average is 

 very low compared with the high average infection of 

 flies bred on infected material, and coupled with the fact 

 that heavily infected flies are sickly and short-lived in 



■ captivity, suggests that under natural conditions also, 

 such heavily-infected flies die off rapidly, and it is only 

 when flies are bred in very lightly-infected material that 

 they survive for any length of time. The occurrence of 

 one or a few ver}^ tiiw embryos encysted in the fat bod}'^ 

 of a fully-matured fly in which no large Habronema occurred, 

 has suggested that, in some cases at any rate, these embryos 

 have been ingested by the fly itself, while feeding on fresh 

 horse dung (fig. 3). In one case a fly bred on cow dung, 

 and kept in cajDtivit}^ for a month, during which time fresh 

 horse dung was placed in the cage for larviposition was 

 found on dissection to contain a ver^^ small Habronema 

 encysted in the fat body (fig. 4). The embryo measured 

 190 f.1 in length by 3.7 /t in breadth. Embryos measuring 

 147 /I to 200 jA,, and in which the gut was undifferentiated, 

 have been taken from a fully-matured captured fly. This 

 stage of the parasite usually occurs in the pupa. 



