58 Gerald F. Hill : 



capacity. Thus enibrvos passed out in the faeces from tlie horse are- 

 taken up by the larvae of Muscae domesctica adults, which have 

 oviposited on the faeces. The faeces remain infective to the fly 

 larvae in this respect up to at least fifteen days after leaving the- 

 rectum. 



Fly larvae are known to react to infection when three days up to* 

 five (lays old, and possibly earlier and later. After a certain 

 amount of development in tlie faeces (c.f. Fig. 38) the embryo of 

 Habronema megastoma enters the larva of Musca domestica, then 

 it continues to develop through the fly pupa and adult fly as seen- 

 in Figs. 40 to 48, in which condition it is ready to complete its-- 

 development in the stomach of the horse; where larvae of such a 

 stage have been met Avith (c.f. Figs. 49 and 49A, and also Table No. 

 4). H. megastoma has not l)een found in any of tlie 182 adult 

 Musca domestica and 6-3 adult Stouioxys calcitrans cauglit in the- 

 stables during the period May-November, 1917. 



In its three last stages in the body of the fly H. megastoma may 

 be differentiated from both H. musca and H. microstoma in corre- 

 sponding stages of development. 



General Summary, Comparison, and Discussion. 



Intermediary host. 



It has been shown that each of tlicse three species of Habrone.ma- 

 found adult in the horse, H. muscae, H. megastoma and H. micros- 

 toma require for the completion of their life-cycle that they shall" 

 enter the body of a fly; in the case of H. muscae, Musca domestica ;- 

 in H. megastoma also Musca domestica; and in H. microstoma, 

 Stomoxys calcitrans, or very rarely under experimental conditions, 

 Musca domestica, i.e., H. mu.scae and H. megastoma find their 

 intermediary host in a non-piercing sucking fly, as distinguished' 

 from H. miprostoma, which finds its chief host (at least) in a pierc- 

 ing sucking fly. The possible importance of this distinction will 

 be referred to a little later. 



It is, of course, quite possible that species of flies other than those- 

 experimented witli, as herein recorded, are involved in the carriage 

 of these Helminth parasites, but time and availability of material' 

 has not so far allowed of experimentation with them. For example, 

 Musca australis, which in the writer's opinion, is likely to be a fre- 

 quent carrier of Helminth infection, has not been experimented 

 with, ''clean" flies not being available at the time the helminth 

 material was at hand. In this connection it is of interest to note- 



