Insects and Parasitic Diseases. 21 



<0.089 mm. long by 0.0066 mm. wide, which was found in fresh horse 

 iaeces collected in a stable yard on October 11th, 1917. While 

 -this and many other embryos found under the vsame conditions 

 have not been identified, there is little doubt that they are some 

 species of Habronema. In this embryo there was. a conspicuous 

 nucleus at about 0.036 nun. from the anterior end, and a smaller 

 one nearer the posterior end. It was not enveloped in a sheath or 

 -shell. 



Two other embryos, each enveloped in a sheath, found in the 

 same lot of faeces, measured 0.0925 mm. and 0.09 mm. in length 

 respectively. In each the sheath was rather closely applied to the 

 body except at the posterior end, where it was held away by the 

 <-urved tail. The outline of the head could not be clearly seen in 

 either of the embryos, but it appeared to be as shown in Fii;. 2. 



Development of the emhryo in faeces. 



No apparent development of the embryo takes place during its 

 passage through the intestines of the horse, the embryos found 

 in the uterus being indistinguishable from those found in fresh 

 horse faeces. A certain amount of development does, however, 

 take place during the life of the embryo in faececs. Fig. 3 shows 

 an embryo obtained from a gravid female, which, with many other 

 •^embryos, Avas incubated in sterilized horse faeces for a period of 

 ;'six days at room temperature. This embryo, which measured 

 O.OSG mm. long by 0.065 nmi. wide, Avas enclosed in a sheath 

 "0.109 mm. long. The pharnyx, folloAved by a bi-lobed clear area 

 and a granular and nucleated mass along the middle line of the 

 body, could be fairly distinctly seen. Tlie large nucleus was 0.036 

 mm. from the anterior end. Other embryos examined measured 

 from 0.072 mm. to 0.0(S6 mm. long by 0.0066 nun. wide, each being 

 enclosed in a sheath measuring from 0.0825 mm. to 0.109 mm. 

 long. 



It is not known whether the embryos enter the fly larvae for- 

 cibly or Avhether they are ingested passively. Ransom considers 

 that the latter is the more plausible theory, and in this I concur. 



The early stages of Habronema muscae in the ijitermediary host 



(Musca domestica). 



In larvae of M. domestica. 



The earliest stage in Avhicli H. muscae are known to occur in the 

 larvae of Musca domestica is shoAvn in Fig. 4. This embryo, Avhich 



