101 



material. Flies hatching out from eighteen to nineteen days 

 later contained larvae. 



Adult files. — The rate of development of the worm larvae 

 within the developing larvae and pupae of Stomoxys calciltrans 

 appears to depend largely upon temperature. Flies bred at 

 a low temperature, 20° to 22° C, and taking about thirty 

 days to hatch out, show larvae in the earlier stages of develop- 

 ment situated usually in the abdomen. Flies bred at a 

 higher temperature, 25° to 26° C, develop more quickly, from 

 seventeen to twenty days, and when hatching out show larvae in 

 the final stage of development, mostly situated in the head and 

 proboscis, with only a few in the abdomen. Those larvae situated 

 in the abdomen are usually in an earlier stage of development. 



If larvae in the final stage of development are found in 

 the proboscis of newly-hatched flies, when flies of the same 

 batch are examined a week to ten days later the larvae pre- 

 sent are often dead. 



If the development of the fly larvae has been delayed it 

 is noticed that when the adult fly hatches out many dead and 

 degenerating worm larvae are present. This was noticed, for 

 example, in a culture in which the fly larvae developed quickly 

 and the adult flies hatched out in from seventeen to twenty 

 days. Some of the fly larvae, however, developed more slowly, 

 and the adult flies hatched out in from thirty to thirty-four 

 days. It was in these flies hatching out later that dead 

 and degenerating worm larvae were found. 



For the most part., newly-hatched flies showed larvae in 

 the earlier stages of development situated in the abdomen. 

 These larvae developed into the final stage in from five to 

 seven days, and migrated to the head and proboscis. Larvae 

 in an earlier stage of development have at times been found 

 in the proboscis along with larvae in the final stage of develop- 

 ment. The larvae were situated in the muscular portion of 

 the bulb of the proboscis, and numbered from thirty to forty. 



At no time did one fail to produce an infestation of 

 Stomoxys calcitrans with larvae of H . microstoma. 



Attempts to produce an infestation in Musca domestica 

 usually gave negative results, but in one case there was 

 an aberrant development of larvae of H. microstoma in M. 

 domestica. In this case many of the flies examined showed 

 embryos and larvae in varying stages of development. The 

 development was distinctly aberrant, the larvae presenting 

 appearances very different from those seen in Stomoxys cal- 

 citrans. Many of the forms present resembled embryos just 

 escaped from the egg-membrane, only were somewhat longer. 

 None of the embryos developed into the thick, nucleated larvae 

 as seen in the normal development. The longer forms were 



