Insects and Parasitic Diseases. 41 



larvae similar in all respects to the one just described and the 

 parasite illustrated in Fig. 29. 



The larva illustrated in Fig-. 29 was i-elatively much longer and 

 narrower than that shown in Figs. 27 and 28, but there was other- 

 wise little marked developmental change. The worm figured (Fig. 

 _29),, measured about 0.435 mm. long by 0.04 mm. wide at the base 

 •of the oesophagus and at the rectum. Scattered nuclei were seen 

 in the oesophagus, intestine and body wall, those in the anterior 

 portion of the body being few and scattered. At about 0.07 mm. 

 from the anterior end there was some indication of a nerve ring. 

 The base of the oesophagus was 0.165 mm. from the anterior end of 

 the body, and at its base there was a slight dilation of the intestine. 

 The anus w^as siinilar to earlier stages, but the tail was distinctly 

 rounded. This larva is comparable with the stage of H. muscae 

 represented in Fig. 9; the latter, however, was 0.115 mm. longer 

 than the present specimen of H. microstoma. 



The larva shown in Figure 30, altliough somewhat shorter than 

 the preceding one, was evidently in a slightly more advanced stage 

 •of development. It measured 0.34 mm. long by 0.056 mm. wide 

 at the rectum. The base of the oesophagus was 0.2 mm. from the 

 anterior end, at which point the body was 0.05 mm. in diameter. 

 The tip of the tail Avas 0.046 mm. from the anus. This larva was 

 one of thirty or more found on January 4th, in tlie head of a 

 Stomoxys pupa from the same culture as the two preceding ones 

 (Experiment No. 12, page 26). 



The next stage known to tlie writer is shown in Fig. 31. The 

 Avorm figured was one of 35 larvae found in a Stomoxys fly 

 (January 10th) from the same culture as the preceding stages (i.e.. 

 Experiment No. 12, p. 31). It measured 0.95 mm. long by 0.04 

 mm. wide at the base of the oesophagus. The base of the pharnyx 

 and oesophagus w^ere respectively 0.03 mm. and 0.38 mm. from the 

 .anterior end of the body. The anterior end of the oesophagus was 

 ■about 0.01 mm. in diameter, increasing at the base to about 0.016 

 mm. At about 0.092 mm. from tlie anterior end there was a con- 

 spicuous nerve ring followed by a group of large nuclei. The 

 anus, still closed, was about 0.043 nmi. from the tip of the tail. 

 The moulting cuticle completely enveloped the worm. This parasite 

 was twenty days old, not- more than seventeen days of which period 

 may have been passed within tlie body of the fly, and it most 

 resembled that stage of H. muscae illustrated by Fig. 14; the latter 

 measured, however, 0.485 mm. longer than the former, but was 

 .apparently less developed. As previously stated (page 25), it was 



