Insects and Parasitic Diseases. 58 



ing 0.21 mm. and 0.25 mm. long respectively. Both were 

 apparently in the same stage of development. 



Had the fly larvae in this culture developed at tlieir usual rate of 

 progress, they should have been well advanced pupae instead of 

 larvae on December 2l8t. Presumably, therefore, the larval H. 

 rnegastoma should ordinarily attain tlie stage of development shown 

 in Fig. 39, whilst its intermediary host is in the pupal stage. 

 Although older and shorter, the larval parasites just referred to 

 were considered to be in a stage of development most comparable 

 with the H. muscae larva shown in Fig. 6. 



It is assumed from the examination of a parasite which was 

 found on November 6th in an adult fly from Experiment No. 17, 

 that an intervening moult takes place before the parasite reaches 

 the stage figured in Fig. 40. The larva measured 0.28 mm. long 

 by about 0.04 mm. wide near the rectum, and about 0.038 mm. 

 wide at the base of the oesophagus, which was 0.115 mm. from the 

 ■anterior end of the body. The moulting cuticle at the anterior end 

 •of the body appeared as shown in Fig. 40, whicli illustrates a larva 

 found in a fly on the same day and from the same culture. Unfor- 

 .tunately the specimen referred to was lost before a drawing and 

 further details could be secured. As will be seen by reference to 

 Experiment No. 17, this parasite was twelve days old. The whole 

 ■of this period may have been passed within the body of the inter- 

 mediate host, but this is very improbable, as will l)e seen in the 

 following paragraph. 



The parasite shown in Fig. 40 was found, as already stated, on 

 November 6th in an adult fly from the same culture as the para- 

 sites shown in the preceding paragraph; it was therefore twelve 

 days old, and may have passed that length of time in the inter- 

 mediary host. This larva measured 0.33 mm. long by about 0.038 

 mm. wide at the base of the oesophagus, which was 0.128 mm. from 

 the anterior end of tliebody. The pharynx was 0.01 mm. in 

 length, and surrounded at its base by a clear space or vacuole. The 

 oesophagus was 0.012 mm. in diameter at the anterior end, and 

 somewhat lai-ger near the base. Numerous moderately large nuclei 

 were seen in the Avhole length of the alimentary tract. A group of 

 •similar nuclei occurred also at about 0.065 mm. from the antei'ior 

 end of the l>ody, and elsewhere in the body wall, as shown in Fig. 

 40. The woi-m had evidently nearly completed a moult. 



The larvae illustrated in Fig. 41 and Fig. 42, also taken from 

 an adult fly, had the same histoi-y as the one shoAvn in Fig. 40. 

 The forme]- measured 0.36 mm. long by about 0.040 mm. wide at the 



