26 Gerald F. Hill: 



been reared entirely on faeces from the rectum of a horse believed^ 

 after a post-mortem examination, to he infected with Habronema- 

 muscae only. The fly larva was ten days old at the time of exami- 

 nation, its growth and development having been retarded by low 

 temperature and insufficient nourishment. 



In the following stage the vacuole or clear space surrounding 

 the pharynx disappears, but the anal operculum remains, thu^- 

 agreeing with Ransom's description of his Stage 4 (1913, p. 20). 

 The pharynx is much longer and distinctly wider than in the pre- 

 ceding stage. The oesophagus is also nmch longer. There is still 

 no indication of the future spinous tip to the tail. A typical larva 

 in this stage of development measured 1.848 mm. in length, by 

 0.05 mm. in width at the base of the oesophagus. The pharynx- 

 was nearly 0.043 mm. in length, and had an oral opening similar 

 to that of the larvae represented in Fig. 15. The nerve ring and 

 base of the oesophagus were 0.12 mm. and 0.64 mm. respectivel}^ 

 from the anterior end of the body. The anus was about 0.079 mm. 

 from the tip of the tail, the processs of moulting was nearly com- 

 plete. The worm was found in the abdomen of a fly from the- 

 same culture as the parasites shown in Figs. 12 and 14. The fly 

 emerged, and was examined on January 9th; the parasite was, 

 therefore, about nineteen days old, and had lived in its inter- 

 mediate host for not more than thirteen days. 



In the next stage (Ransom's Stage 5), the spines at the tip of the- 

 tail are seen under the cuticle and the rectum is distended as in 

 earlier stages, and as recorded by Ransom (1913, p. 21). A larva in 

 this condition was found on the same date in the same culture as 

 that described in the preceding paragraph (i.e., a larva agreeing- 

 with Ransom's Stage 4). It measured 2.013 mm. in length by^ 

 about 0.056 mm. in width at the base of the oesophagus. The- 

 pharnyx was nearly 0.043 nmi. in length. From the anterior end" 

 of the body the nerve ring and base of tlie oesophagus Avere distant 

 0.122 mm. and 0.775 mm. respectively. Tliis worm was found in 

 a cyst in the alidomen, and was about to moult. 



Fig. 15 represents a larva in the condition designated Stage- 

 6 by Ransom, which is the final larval stage of Habronema muscae' 

 found in the fly. It was reared from a culture of embryos taken 

 from a gravid female on January 11th, and incubated in sterilized' 

 faeces for five days (i.e., until January 16th), when the embryo- 

 infected faeces were fed to fly larvae, which hatched on January 7th' 

 and emerged as flies on January 30th. The parasite was there- 

 fore nineteen days old, not more than fourteen days of whiclr 

 period were spent in its intermediate host. 



