97 



light, temperature, and bacterial growth. They rarely show 

 any tendency to leave the shells. When placed in tap water 

 the majority of the embryos are found to be free in twenty- 

 four hours. 



Adult flies. — At first the observations were confined to 

 the study of the development of H. muscae in Musca 

 domestica. In the preliminary experiments it was found that 

 approximately 100 per cent, of the flies hatching out showed 

 larvae situated, almost invariably, in the head and proboscis. 

 These larvae were found to resemble the sixth larval stage of 

 H . muscae, as described by Ransom. As many as eight larvae 

 were found in the head and proboscis of one fly. 



In the later experiments the examination of flies that had 

 just hatched often showed the presence of larvae in an early 

 stage of development, measuring approximately 400 ju, long, 

 and being situated in the abdomen, and usually encysted. In 

 from five to seven days these larvae were found to have 

 developed into the final larval stage, and to have migrated 

 to the head and proboscis. As many as from thirty to forty 

 larvae have been found in the head and proboscis of these flies. 



For the most part larvae found in the head and proboscis 

 have been of the final larval stage of development, but occa- 

 sionally larvae of an earlier stage of development have been 

 found along with those in the final stage. 



The flies often showed a marked paralysis of the proboscis, 

 although they were still able to feed. 



The time occupied in development from the deposit of the 

 eggs to the hatching of the adult flies was usually from fourteen 

 to eighteen days. 



Flies bred in sterilized horse-dung, with which had been 

 mixed an emulsion of embryos in normal saline solution, 

 usually showed the presence of larvae in the great majority of 

 those hatching out. On three occasions, however, no larvae 

 were present in any of the flies hatching out. On two of these 

 occasions the emulsion of embryos was made in tap water, and 

 on one occasion in saline solution. On each of these occasions 

 the eggs were obtained from flies caught in the laboratory. 

 There was never any failure of development of larvae in the 

 strain of Musca domestica kept going by artificial cultivation. 



All attempts to obtain any development of embryos of 

 H . muscae in Stomoxys calcitrans failed. 



Larvae of H. muscae. — Attention was practically confined 

 to the study of the final larval stage. These larvae obtained 

 from the head and proboscis of flies were found to measure 

 from 2'58 mm. to 2;§7 mm. long, the majority measuring 

 2'7 mm. The maximum width was found to vary from 50 /a 

 to 66*6 fx. The head was rounded and the body tapered slightly 



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