99 



Larvae were found to remain alive in the bodies of dead 

 flies for several days if loss of moisture was prevented. 



The Life-history of Habronema megastoma 

 (Rudolphi, 1819). 



The methods adopted in this investigation have already 

 been mentioned. The embryos were sometimes obtained from 

 the contents of the submucous tumours and sometimes from the 

 gravid female. 



Embryos of H . megastoma. — The embryos are enclosed in 

 a thin shell or membrane. They are doubled on themselves in 

 the shape of the letter U, the tail coming to lie close to the 

 head. The shell measures from 43*3 /x to 53*3 jx long by 

 116 jix to 13*3 /x wide. The widest portion of the embryo 

 measures 6'6 /x. 



The embryos when placed in saline solution and tap water 

 behave in the same way as those of H. muscae. When they do 

 break away from the shell they remain bent in the shape of 

 the letter V or the letter L. They are only very slightly 

 motile. When taken from the gravid female the shell is less 

 resistant than in those born under natural conditions. This 

 has been found true of the embryos of all three species. 



Adult Flies. — In the main the results of the observations 

 were the same as in the case of flies infested with the larvae of 

 Habronema muscae. The rate of development of the larvae 

 appeared to depend upon the temperature at which the culture 

 was kept. During the warmer weather flies hatching out often 

 showed larvae at or near the final stage of development. At 

 other times larvae were found in a very early stage of develop- 

 ment. In one case flies hatching out in seventeen days showed 

 larvae measuring from 2 72 '7 jx to 409 /x in length. These 

 larvae were present in the abdomen, and the majority were 

 encysted. From four to five days later these larvae had 

 developed into the final larval stage. The atmospheric 

 temperature was high during this latter period. When the 

 final larval stage was reached few or no larvae remained in the 

 abdomen, but migrated to the head and proboscis. Many of 

 the flies died suddenly, probably through injury to the central 

 nervous system by the migrating larvae. The parasitism was 

 very heavy, from fifty to sixty larvae being present in a single 

 fly. The proboscides of many of the flies were seen to be 

 paralyzed. When these flies were examined some days later 

 the larvae were found to be less active than when first making 

 their appearance in the ]iead and proboscis. 



It has been observed that if flies die when the larvae are 

 in an early stage of development these larvae quickly die, but 

 if the final larval stage has been reached the larvae live for 

 e2 



