52 Gerald F. Hill: 



fifteen days at a temperature uf 22°-2T ('. (c.f. Experiment No. 19^ 

 page 47). llie parasite shown in Fig. 38a, which was not enclosed 

 in a sheath, measured about 0.0528 mm. long from tlie bend in 

 approximately the middle of tlie body to the aiiteiioi- end, by about 

 0.0065 mm. in diameter at its widest part. A large nucleus occurred 

 at about 0.043 mm. from tlie anterior end, and a smaller one was 

 seen postei'ior to the fii'sl. In some specimens one large nucleus, 

 only was seen, and in others there Aveie one or two nuclei as above,, 

 and one smaller nnclLUs at about 0.039 mm. from the posterior end- 

 Other embryos enclosed in sheath or egg-shell were found on the- 

 same day and in tl:e same culture. The embryo shown in Fig. 38b 

 measured about 0.104 mm. long from the anterior end to the tip- 

 of the tail. The body was bent in the middle in the characteristic 

 manner, and the laige nucleus was somewhat further back than 

 usual, i.e., 0.053 nun. from the anterior end. Posterior to what 

 was evidently the rudimentary pharynx there were two clear spaces, 

 which were also ob^^erved in the specimens shown in Fig. 3()f and 

 Fig. 38a. Posterior to these clear spaces and in the middle line 

 of tlie anterior fourth of tlie body was a noticeable aggregation 

 of minute granular })odies, probably the earliest evidence of the' 

 developing alimentary system. 



Devdopment in ihe larvae of M. Jofnesfica. 



Early larval stages of H. megastoma comparable with the stages of 

 H. microstoma illustrated by Figs. 20, 21, 22, and 23, have not 

 been found. The earliest stage known to the writer to occur in the 

 intermediate host is shown in Fig. 39. This parasite was found in 

 a fly larva on December 21st from a culture of sterilized faeces, 

 which was infected on December 3rd, with the contents of a stomach 

 tumour, and then incubated for a period of seven days before being 

 exposed to ingestion by the fly larvae than five days old (c.f. Experi- 

 ment No. 19, page 47). The parasite was therefore eighteen days 

 old, eleven days of which period may have been passed in the body 

 of the fly larvae. The true period was, however, probably much 

 shorter (see text referring to Fig. 43). The length of the worm was 

 0.221 mm., and the width near the rectum about 0.046 mm. The 

 base of the oesophagus was 0.099 mm. from the anterior end of 

 the body, and the tip of the tail about 0.042 mm. from the anal 

 operculum. 



Two other larvae from the same culture, examined on the same 

 day as the above, were each found to contain one parasite measur- 



