96 



Habronema megastoma was found to be of infrequent 

 occurrence, and less commonly met with than the other species. 

 Sometimes one would obtain two or three stomachs consecu- 

 tively which contained H. megastoma, and then many 

 stomachs would be examined before obtaining another speci- 

 men. It was not until after a large number of stomachs had 

 been examined that it became obvious that H. megastoma 

 was more rarely met with than H . microstoma, H. muscae 

 being the most common, and usually found in each stomach 

 examined. 



For the purposes of the subject under investigation it 

 was considered that any detailed study of the adult forms 

 was unlikely to give any useful information. 



No detailed study of the development of the worm larvae 

 in the fly larvae, pupae, and adults was made, as, of neces- 

 sity, a limit had to be placed on the scope of the investigation. 



The following is a brief outline of the observations made 

 on the embryos and larvae of the three species of Habronema 

 and examination of adult flies : — 



The Life-history of Habronema muscae (Carter, 1861). 



Ransom has already shown that embryos of Habronema 

 muscae, passed along with the faeces of the horse, gain entrance 

 to the larvae of Musca domestica, probably through being 

 swallowed by the fly larvae. The embryos gain the body 

 cavity, where they pass through their larval stages, and have 

 usually reached the final larval stage (sixth stage of Ransom) 

 at or soon after the hatching of the adult fly. This final 

 larval stage was the first stage to be observed in the stomach 

 of the horse. 



Ransom's work consisted mainly in the examination of 

 adult flies, pupae, and larvae for the presence of larvae of 

 Habronema. He assumed that all larvae found in the head 

 and proboscis of adult flies were larvae of Habronema muscae. 

 It is possible, however, that some of the specimens he 

 observed may have been larvae of Habronema megastoma. 



The experiments undertaken in 1916 under artificial con- 

 ditions confirmed Ransom's conclusions. 



Embryos of H . muscae. — Embryos that have been passed 

 out from the female have been found to be enclosed in a thin 

 shell which is closely applied to the body except at the 

 posterior end, where it is distinctly seen held away by the 

 curved tail. The embryos are only slightly motile. They 

 measure from 80 /x in length by 12 jul in width to 

 110 /x in length by 6'6 fx in width. When these embryos are 

 collected from the stomach contents or from the gravid female 

 and placed in saline they live for many days, depending on 



