Insects and Parasitic Diseases. 51 



111111. wide respectively. Fig. 36d shows the young embryo in a 

 condition sufficiently far advanced to enable it to be definitely 

 distinguished from embryos of H. muscac and H. microstoma by 

 •the relative position of the anterior to the posterior end. As will 

 be seen on comparing Fig. 1, of H. muscae, Fig. 18, of H. micros- 

 toma, and Fig. 36, of H. megastoma, the tail of the young embryo 

 in the first species never reaches more than half-Avay along the main 

 part of the body when bent in the egg. In H. microstoma, though 

 .a stage comparable wdtli Fig. le is not shown, it does occur. In 

 H. megastoma, hoAvever, the embryo is seen to be bent in about the 

 jniddle of its length in several stages. Thus the parasite as it 

 leaves the parent worm, as well as in some subsequent stages (as 

 will be seen later) contrasts in a marked degree with H. muscae and 

 H. microstoma. 



In the stage shown in Fig. 36d, the embryo measured 0.056 mm. 

 long by 0.0165 mm. wide.v 



Still further development is seen in Fig. 36e, which measured 

 ♦0.056 mm. long by 0.018 mm. wide. Fig. •36f shows an embryo 0.057 

 mm. long by 0.017 mm. wide in the most advanced stage attained 

 in the uterus of the parent Avorm. As is the case witli the other 

 ^species dealt Avith in this report the form of anterior end can be 

 made out only Avith difficulty. At the anterior end there is evi- 

 'dence of a horn-like pi'ocess, and a rudimentai-y pharynx Avith an 

 adjacent clear space as in H. muscae, b\it the more or less con- 

 spicuous nuclei observed in H. muscae and H. microstoma have not 

 .been observed in such young embryos of this species. 



Deuelojfmenf of the emhrijo in the tumour. 



Further development takes place during the life of the embryo 

 in the purulent matter contained in the stomach tumour. The 

 •embryos illustrated in Fig. 37 Avere found in such circumstances as 

 AA'ere others Avhich had I'uptured the egg-shell or sheath. 



TJevtlopment of the embryo in faeces. 



Doubtless the cmbi-yo is carried into the stomach of tlie hoi'se 

 Avith the purulent discharge from the several openings in the 

 summit of the tumour, but eml.>ryos Iuia^' not been identified in thw 

 ■stomach or intestines nor in the faeces of natui-ally infected horses. 



The development Avhicli ]>vol^al,ly t;'kes ])la(e in tlie fneces. is 

 illustrated in Fig. 38. a and b. Tlies'> enibi-yos, taken fi-oni an 

 -adult Avoj-ni. were incubated in sterilized faece< foi- a period of 



