54 Gerald F. Hill : 



base of the oesophagus, i.e., at 0.12 iimi. from the aiitei-ioi- end of 

 tlie body. Another worm of tlie same total lengtli and from the 

 same fly measured 0.145 mm. from the anterior end of tlie body to 

 the base of the oesophagus. Tlie \vorm sliown in Fig. 42 was 0.37 

 mm. long by about 0.040 'mm. wide at the base of the oesophagus, 

 which was 0.14 mm. from the anterior end of the body. In these- 

 three worms and most others in a similar stai^e of dev-^lopment the 

 cuticle at the anterior end was somewhat separated from the body,.. 

 as seen in Figs. 41 and 42. The nuclei in the alimentai-y tract 

 were fewer and smaller than those seen in the larva illustrated in 

 Fig. 40, apparently indicating that the latter was hardly so far 

 advanced, since these nuclei are at their maximum almost if not 

 (piite as soon as they are first noticeable. Evidently this stage (c.f. 

 Figs. 41 and 42) is comparable with Kanso'm's Stage 1 of H. muscae- 

 and also with the eight-day-old larva (H. muscae) shown in Fig. 8' 

 of this Report, both of whicli were froin fly pupae. 



The parasite illustrated in Fig. 4-3 was evidently in a more- 

 advanced stage than the larvae illustrated in Fig. 41 and Fig. 42. 

 It was found on November 8th in a fly from the same culture as 

 the latter, and was, therefore, fourteen days old. The body was- 

 0.5 mm. long by about 0.04 mm. wide at the base of the oesophagus, 

 which was about 0.17 mm. from the anterior end of the body. The 

 pliarynx, which was about to moult, was about 0.015 mm. long, and' 

 a clear space surrounded it. Nuclei were seen in the body wall 

 and alimentary tract, but they were not made out in that part of 

 the body where, in later stages, the nerve ring is to be found. This 

 stage is near that stage of H. muscae designated by Ransom as 

 Stage 2. 



The next stage in development of the larva known to the writer 

 is shown in Fig. 44. The pnrasite was found on December 20th in 

 an adult fly from the same culture as the parasite shown in Fig. 

 39, which was found in a fly-larva on December 21st (c.f. p. 52)' 

 and also Experiment No. 19, page 47.) llie latter (Fig. 39), 

 therefore, may have lived one day longer in the intermediate host 

 than the former (Fig. 44), but as it was considerably less developed 

 it may be assumed that its life in the intermediary was at least 

 several days less than that of the more developed specimen. The 

 larva (Fig. -14) measured 0.87 nun. long l)y 0.04() mm. wide near 

 the base of the oesophagus. At the base of the pharynx, which was 

 about 0.016 mm. from the anterior end, the body was 0.029 mm. 

 in diameter, increasing to about 0.06 mm. at the base of the 

 oesophagus. The oesophagus measured 0.013 mm. in diameter at 



