22 Gerald F. Hill: 



is four and two-third days old, was found in the alimentary canal' 

 of a Musea doniestica larva, tlien five days old. The embryo was 

 one of jnany which had been taken from a gravid Habronema 

 nmscae, and incubated in sterilized faeces at a temperature of 

 22 °C. for 42 hours, at the end of which period they and the faeces- 

 were offered to fly larvae, then 48 hours old. 



The embryo measured 0.0905 mm. in length by 0.0066 nun. in 

 breadth, and agreed closely with the specimen shown in Fig. 3,. 

 excepting that it was free and not enclosed in a sheath. 



Great difficulty is experienced in finding these embryos in fly- 

 larvae, owing to their small size and transparency, and the nature- 

 of the debris surrounding them. The occurrence of other' species of 

 nematode Avorms in fly larvae, which, as Ransoim has pointed out, 

 aggriavates this difficulty, has been obviated by the technique- 

 employed in these experiments. 



In fwpae of M. domestica. 



Nothing is known of the further development which takes place- 

 in the young nematode larvae until the stage shown in Fig. 5 is 

 reached. The specimen shown in Fig. 5 measured 0.25 mm. in 

 length by 0.05 mm. in breadth at the posterior end of the oeso- 

 phagus. The sliallow mouth cavity appears to be followed by the 

 oesophagus, but this structure could not be clearly seen owing to 

 the fact that the cuticle was separated from the body at the anterior 

 end, showing tliat the larvae was in process of moulting. It will 

 be noted that in general appearance, this larva (measuring 0.25- 

 mm. in length) agrees, closely with the stage designated Stage 1 by 

 Ransom (1913, p. 16), which measures from 0.4 mm. to 0.45 mm. in 

 length (see later figures). 



The same fiy pupa contained two other larvae, a younger one- 

 measuring 0.2 mm. in length, which was not in process of moult- 

 ing, and an older one, measuring 0.65 nun. in length (see Fig. 9). 

 The embryos which produced these larvae w^ere obtained from a 

 gravid H. muscae on November 26th, mixed with saline solution 

 and a small quantity of sterilized faeces, and fed to fly larvae 

 which hatched on November 23rd. The pupa was examined on 

 December 3rd ; the oldest parasite was therefore not more than- 

 seven days old. 



The next stage in the development of the larvae is shown in Fig.. 

 6. This larva, from a fly pupa, was found on December 4t]i in 

 the same culture as those referred to in the preceding paragraph. 



The shallow oral cavity is followed by a straight pharnyx, which 



