Insects and Parasitic Diseases. 25 



The length of the parasite was about 1 mm. (1.07 mm.) by 0.05 

 jnm. in width at the posterior end of the oesophagus, which was 

 >0.35 mm. from the anterior end of the body. Tlie intestine was 

 0.62 mm. in length, followed by a pyriform rectum. The oper- 

 culum like apex of the rectum was about 0.06 nun. from the tip of 

 the tail and nearly level with the cuticle of the body. The intestine 

 was 0.015 mm. diameter at the base of the oesophagus, increasing 

 to about 0.03 mm. at about 0.07 mm. from its anterior end, 

 i:hen decreasing to about 0.015 mm., which diameter was main- 

 tained to near its junction with the rectum. 



These parasites were evidently in the stage figured and designated 

 ^tage 2 by Ransom (1913, p. 18). It must be remarked, however, 

 that in both parasites referred to in the preceding text nuclei were 

 plainly seen in the rectum (see Figs. 12 and 13A, whereas Ransom 

 remarks of his larva of Stage 2, *' nuclei like those seen in the wall 

 of the remainder of the alimentary tract are absent from the 

 rectum." 



/// adult M. domestica. 



Very definite progress m development is seen in the larva repre- 

 .sented by Fig. 14, Avhich was found in an adult fly from the same 

 culture as the parasite shown in Fig. 12 and discussed above. 



The fly emerged and was examined on January 7th ; the parasite 

 was, therefore, seventeen days old. The first six days of its 

 embryonic life were spent in sterilized faeces, Avith similar embryos 

 only, and not more than eleven days in the body of its intermediate 

 host. 



It measured 1.435 mm. in length by about 0.043 mm. in width. 

 The pharnyx, whicli Avas 0.0297 mm. in length, was surrounded near 

 the anterior end by a somewhat clear space. The oesophagus was 

 about 0.013 mm. in diameter at the anterior end, increasing very 

 gradually to a minimum diameter of 0.0198 mm. at its base, which 

 was 0.43 mm. from the oral opening. The conspicuous nerve ring, 

 •surrounded by numerous nuclei, was about 0.12 mm. from the 

 anterior end of the parasite. A few small nuclei occurred in the 

 body-wall and alimentary tract, but these were f.ew and scattered. 



No evidence of a spinous-tipped tail could be seen under the 

 moulting cuticle of this or other larvae of about the same length 

 and condition. This larvae would appear to be in a stage of 

 development near to Stage 3 of Ransom. 



Although larvae of this stage are usually found in adult flies, a 

 similar parasite was found in a Musca domestica larva which had 



