38 Gerald F. Hill: 



ber 26th to 2yth), active embryos were found which measured. 

 aloui 0.1 lum. long by 0.0065 mm. wide. The group of small nuclei 

 observed in the larger embryo refer I'ed U> above were not made out, 

 but a fairly large and conspicuous nucleus was seen in each about 

 0.045 nnn. from the anterior end. The majority of these embryos 

 were enveloped in sheaths, but others were free. On the same 

 day and from the same culture a Musca domestica larva was found 

 to l:>e infected with an embryo measuring 0.099 n\m. long by 0.0065 

 mm. wide, with a nucleus at 0.048 mm. from the anterior end, but 

 otherwise agreeing Avith the forms found free in tlie faeces. 



On December 27th an embryo (Fig. 20) was found in a Stomoxys^ 

 larva which agreed very closely with the one shown in Fig. 19. 

 Botli embryos were from the same culture (i.e., Experiment No. 12,. 

 p. 31). but whereas the later (Fig. 19) was five days old. and liad' 

 lived in faecal matter only, the former (Fig. 20) was six days old, 

 and may have been harboured witliin the fly lai'va for not more- 

 than three days., 



The parasite shown in Fig. 20 measured about 0.115 mm. long 

 by about 0.0066 mm. wide. A very large nucleus occurred at about 

 0.039 mm. from the anterior end, and numerous small ones could 

 be seen occupying the middle line of the body for the greater part 

 of its length. The tail was usually carried bent sharply over, but 

 during the fre(i|uent snake-like movements of the body it was seen 

 to be capable of the freest action. This embryo, like the other from 

 the same culture, was enclosed in a sheath. 



Succeeding stages in the development of the parasite are shown 

 in Figs. 21, 22, and 23. These three, in addition to two embryos 

 similar to the one represented in Fig. 20, were found on Januar;s 

 24th in a Stomoxys larva from the culture referred to in Experi- 

 ment No. 13, p. 32. The latter two were located in the alimentary 

 tract, and were not enclosed in sheaths, the others. Figs. 21, 22 and 

 23, were found in tlie fat-body separating the body wall from the 

 alimentary tract. 



The parasite shown in Fig. 21 Avas about 0.138 mm. long by 

 about 0.02 mm. Avide at the anus. The process at the anterior end 

 noted in earlier stages Avas still evident. An oral opening could 

 not be made out, but a clear space at the anterior end of the body 

 indicated the presence of a pharynx. There Avas no visible alimen- 

 tary tract, the whole of the body being apparently composed of a 

 mass of nuclei of varying sizes, those in the anterior half being 

 largest. The anal opening Avas closed by a rounded projection. 

 Only a portion of the rectum could be seen clearly. The tail, Avhich 



