56 Gerald F. Hill : 



day the culture was offered as food to three-days-old larvae of H. 

 doniestica. It was therefore tliirteeii days old, the whole of which 

 period may have been passed within the body of the intermediary 

 host. The worm was 1.650 mm. long by about 0.03.3 mm. wide at 

 the base of the pharynx, and 0.053 mm. wide at the base of the 

 oesophagus. The base of the pharynx and oesophagus were about 

 0.033 mm. and 0.428 mm. respectively from the anterior end of the 

 body. The anal opening, which was 0.069 mm. from the tip of the 

 tail, was still closed as in earlier stages. 



The next stage in the development of the larval parasite is illus- 

 trated by Fig. 47 (c.f. Table No. 3, Specimen No. 2). The speci- 

 men here figured was 1.848 nmi. long by 0.082 nmi. wide at the base 

 of the oesophagus, ie. , at 0.56 mm. from the anterior end of the 

 body. The base of the pharynx and the nerve ring were 0.04 mm. 

 and 0.132 mm. respectively from the anterior end of the body. The 

 anus was still closed, minute spines were evident beneath the cuticle 

 at the tip of the tail, indicating that this stage is comparable with 

 the larval stage of H. microstoma referred to on page 42 of this 

 Report, and with Ransom's 5th stage of H. muscae. This larva 

 was encysted in the abdomen of a fly found on the same day and 

 in the same culture as the parasite in Fig. 46 (c.f. ?]xperiment No. 

 20, p. 48); it was therefore thirteen days old, and may have lived 

 for the whole of tliat time in the body of the intermediary fly. It 

 was about to moult. 



The final larval stage in the body of the intermediate host is seen 

 in Fig. 48 and Fig. 48A (c.f. Experiment No. 20, page 48). The 

 history of this larva was the same as that of the larva shown in 

 Figs. 46 and 47 ; it was therefore thirteen days old. As will be 

 seen, the limit of possible age of the larvae in Figs. 46 and 47, and 

 in 48 and 48A is the same, but there is no doubt in my mind, from 

 the internal tvidence of the stage of development reached bv these 

 two lots of larvae, that those seen in Figs. 46 and 47 were not 

 ingested by the fly larvae so early as was that seen in Figs. 48 and 

 48A, the latter being now undoubtedly further advancj?d, and there- 

 fore obviously older than the former. It measured 2.244 mm. long 

 by 0.096 mm. wide at the base of the oesophagus, which Avas 0.63 

 mm. from the anterior end of the body. The base of the pharynx 

 and the nerve ring were about 0.066 mm. and 0.138 mm. respec- 

 tively from the anterior end of the body. (For other measurements 

 see Table No. 3, Specimen No. 1). The anus, closed in all earlier 

 stages, was open and the tip of the tail was spinous (c.f. Fig. 48A). 



The parasite was in a stage comparable therefore with the larval 



