40 Gerald F. Hill .- 



C— Habronema megastoma (Rmlolphi, 1819). 



1. — Historical. 



As !-:tatL>d in the liitioduction to Part I. of this report nothing 

 •definite appears to have been recorded of the life-history of H. 

 megastoma, eitlier in Australia or elsewhere. 



Apparently (Railliet, 1916, p. 102) some reference is made to the 

 larvae of this worm by Ercolani, 1859, but the paper has not been 

 available to me for study. 



Railliet (1895, p. 535) stat-es that the life-history of this species 

 is unknown, but that there is reason to suppose that the inter- 

 mediate host is an insect found in fodder. The same author (page 

 1)34) states further that Chabert in 1782 recorded H. megastoma as 

 the causative agent of tumours in the stomach of the horse. 



2.— The Adult. 



The adult of H. megastoma is easily separated from its con- 

 geners, H. muscae and H. microstoma, by its smaller size, and the 

 very distinctive form of the anterior end. The worm, however, is 

 so well known that it is quite unnecessary here to describe it in 

 detail. 



It Avould appear from the writer's observations that the adult 

 istages of H. megastoma occur naturally only in tumours in the 

 •<lelinitive host and that tlieir rare occurrence on the external sur- 

 face of the tumour or adjacent membrane is due to their escape 

 from their natural surroundings after the death of the host. The 

 occurrence within the tumours of young larvae, i.e., those in the 

 final stage of development attained in the body of the fly will be 

 referred to later on. 



A census of the nematode parasites found in thirty-nine horses' 

 ■stomachs examined during these investigations shows that nineteen 

 t^tomachs contained well-developed tumours of H. megastoma (c.f. 

 Table 9). 



The adults are also known to occur in the splenic abscesses which 

 appear to have become more common of recent years, and to be 

 responsible for a considerable increase of mortality in horses in 

 -certain seasons and certain districts in South-Eastern Australia. 



3.— Record of Experiments. 



The technique employed in these experiments has been fully 

 <)escribc-d on pages 12-15. 



