42 Gerald F. Hill: 



seventeen days old, and had lived in the body of the fly not morer 

 than eleven days. 



After undergoing at least anotlier moult the minute spines at the 

 tip of the tail are seen under the cuticle. The parasite now 

 measures from 1.419 mm. to l.ooO mm. in length. This stage, which 

 is comparable with Hansom's 5th stage of Habronema muscae, is 

 generally found in the head or abdomen of pupae in an advanced 

 stage of development* 



Numerous larval parasites in this stage of development were 

 found in a pupa on January 29tli, in a culture (Experiment No. 

 lo, page .'^2), which produced also the parasites of Figs. 21, 22 and 

 23. Reference to this experiment will show that the larvae were 

 fifteen days old, and that not more than thirteen days of this period 

 could have been lived within the body of the developing fly. A 

 typical example measured 1.485 mm. long by 0.049 mm. wide at the- 

 base of the oesophagus, i.e., about 0.68 mm. from the anterior 

 end, and about 0.033 mm. wide at the anus. 



The oesophagus was 0.013 mm. in diameter at the anterior end, 

 and increased to 0.030 mm. in diameter at its base. The nerve- 

 ring was about 0.1 mm. from the anterior end and the closed anus 

 about 0.059 mm. from the tip of the tail. The moulting cuticle- 

 adhered somewhat closely to the body. 



After this moult is completed, the spines are evident at the tip- 

 of tail, and the anus is no longer closed by the rounded projection 

 seen in earlier stages. Fig. 32 shows the anterioi- end of a worm 

 in this stage of development, which was found in the proboscis of 

 a Stomoxys fly on January 12th. The parasite was reared from 

 the same culture as those shown in the three preceding figures 

 (Experiment No. 12), and was therefore twenty-two days old, not 

 more than nineteen days of which period may liave been spent 

 within the intermediate host. It measured 1.560 mm., long by 

 0.0495 nmi. Avide at the base of tlie oesophagus, and 0.0297 mm. 

 wide at the anal opening. The length of the pharynx was about 

 0.049 mm. The nerve ring and base of the oesophagus were 

 respectively 0.1 mm. and 0.69 mm. from tlie anterior end. The 

 oesophagus was 0.0135 mm. in diameter at its base. The anterior 

 one-sixth was of fairly uniform diameter, but about 0.11 mm. 

 from its commencement a marked increase in thickness occurred 

 which was maintained tlirough its i-emaining length. 



The tip of the tail, wliicli was about 0.069 mm. from the anal 

 opening, was bluntly rounded, and ornamented with minute- 

 spines. 



