Insects and Parasitic Diseases. 55 



the anterior end, and increased to about 0.02 mm. at its base,. 

 which was about 0.247 mm. from the anterior end of the body. The- 

 anus was evidently still closed as in early stages. The nerve ring^ 

 is now clearly distinguishable, being about 0.073 mm. from the 

 anterior end. A few nuclei were seen near the nerve-ring, and in 

 the body wall. The pharynx and posterior end were moulting. 



Other lai-val parasites, including specimens 4-9, of Table 3, were 

 found in flies from the same culture and on the same day. These 

 parasites measured from 0.98 mm. long in Specimen No. 9, to 1.280 

 mm. long in Specimen No. 4. Possibly all of this series are merely 

 successive steps in the progress of larval development from one 

 definite stage (c.f. Fig. 44) to another (c.f. Fig. 46). All of these 

 most closely resemble the stage of H. microstoma represented by 

 Fig. 14, and therefore Ransom's Stage 3 of H. muscae. 



One of the series of larvae referred to above (Specimen No. 7, 

 Table 3) is shown in Fig. 45. In this specimen the cuticle at the 

 anterior end of the body was transversely ribbed and oral lips were 

 seen distinctly. These two features were not observed in less 

 developed specimens. The anus was closed as in earlier stages. 



The parasite shown in Fig. 46 (c.f. Table No. 3, Specimen No, 

 3) is in a markedly more advanced stage of development than any 

 of the preceding ones. Two very definite, and for the purpose of 

 diagnosis very important, characters manifest themselves in the 

 worm, namely: — (1) The oral cavity is distinctly widened 

 anteriorly, thus simulating the characteristic funnel-shaped 

 anterior end of the alimentary canal of the adult, which character 

 alone is suflicient to distinguish this larval stage of H. megastoma 

 from any stage of either H. muscae or H. microstoma (in both of 

 which species the oral cavity is not so widened); (2) a constriction 

 of the body near the anterior end like that so conspicuous in the 

 adult, is distinctly seen beneath the cuticle of the worm. 



Whether or not a moult occurs just before these developments be- 

 come visible is not known. This parasite (Fig. 46) was found on 

 December 26th, encysted in the abdomen of an adult fly, from 

 Experiment No. 20. It will be seen, therefore, that this stage in 

 the development of H. megastoma can only be compared with the 

 corresponding stages in H. muscae (c.f. Ransom's 4th Stage), and 

 in H. microstoma (my Fig. 31) in that this forms an intermediate 

 condition between Stages 3 and 5, recognised as being comparable 

 in other respects in all three species. 



The embryo from which it was reared was obtained with many 

 others, from a stomach tumour on December 13th, and on the sanie 



