<)2 Gerald F. Hill : 



Neither the excretory opening and its main tube, nor any indica- 

 tion of the developing genital organs has been seen in any of the 

 Jarvae herein described. 



Bull (MSS. IDlJ-^), Avho records having reared H. rnegastoma from 

 tlie einbryonic stage to the " sixth stage," in Musca domestica, con- 

 -siders that in the final larval stage reached in the body of the 

 fly H. megastoma cannot be differentiated from larval H. muscae 

 in the same relative stage of development. The evidence I have 

 -fidduced does not support this conclusion. This investigator used 

 ^ culture of H. rnegastoma (from a tumour) in non-sterilized faeces 

 from a horse Avhich was a})parently not sul>sequently post-mortemed 

 to determine the presence or absence of H. megastoma in the 

 stomach. Previously, however, he bred flies from larvae fed on 

 faeces from the horse, and finding them all negative for Habra- 

 nema he assumed that the horse did not contain Habronema 

 'embryos. Some of my experiments, notably Experiment No. 18, 

 page 47, show tliat flies may be reared from faeces known to be 

 infected and yet, on examination, prove to be negative for 

 Habronema. The possibility that Bull Avas dealing with H. muscae 

 -ind not H. megastoma is therefore not excluded. 



As to the path taken by these Helminth larvae within the fly from 

 the time the larvae are ingested by the fly-larvae, the evidence is 

 not as complete as could be desired. I can say, however, that Avith 

 •Tegard to H. muscae and H. microstoma, the youngest larvae of 

 "these species, found in the larvae (tf Musca domestica in the former 

 -case, and in larvae of Stomoxys calcitrans in the latter, occur in 

 the alimentary canal. 



The next succeeding stages in each case are found either free in 

 the body cavity or encysted in the fat-body of the larvae. No young 

 stages of H. megastoma corresponding to the above are yet known 

 "in the larvae of M. domestica. In the pupa the helhiinth larvae 

 are still found free or encysted in the broken-down tissues. 



The exact position taken up by the developing pai'asitic larvae 

 in the tis.sues of the pupa and early imago have not^ yet been deter- 

 mined. In flies that have emerged from the pupal case, the para- 

 •sites in the case o^f H. muscae and H. microstoma have been found 

 free in the body cavity of the abdomen, thorax, and head of the 

 fly-host, and also encysted in the tissues surrounding the alimentary 

 -canal and on the surface of the tracheae. This is also true of H. 

 luegiistoma, except that the solitary example of the '' 6th stage " of 

 this parasite found in the fly host (M. domestica) was free. 



