Insects and Parasitic Diseases, 19 



f(rostrum) is not unusual (Fig. 17). The greater proportion were 

 found in the post-erior part of the liead capsule. 



Ransom (1913, p. 13), states that the largest number of larval 

 worms he found in an individual fly was eight, though, as he 

 remarks. Carter (1831) noted as many as twenty in one fly. 



The largest number of larvae, almost certainly H. muscae, found 

 by the writer in a naturally infected fly (i.e., a fly caught in the 

 .stable) was three, but flies reared in the laboratory from larvae 

 fed upon artificially infected faeces have produced a much greater 

 number of parasites. Under these conditions 25 to 30 larval H. 

 muscae in a, single fly is not an unusual occurrence, while from one 

 fly 72 of these parasites Avere obtained. 



D. The viability of embryonic Habronema muscae in faeces. 



It has been shown (Experiment No. 1, p. 8), that embryonic 

 Habronema muscae removed from the uteri of gravid worms and 

 incubated in sterilized faeces at a temperature of 22°C., may retain 

 iiheir viability and are capable of infecting fly larvae for a period 

 -of eight days. 



In view of the results of similar experiments with the embryos 

 of H. microstoma (see later Experiment No. 10, p. 2G), it seems 

 possible that this period may be considerably lengthened. Under 

 the most favourable natural conditions it is conceivable that 

 .embryos may retain their viability for equally long periods. 



.K. To determine the period of survival of larvae removed from 

 flies. 



On January 7th, ten larval H. muscae from the abdomen of a fly 

 were placed in saline solution in an open dish. On the following 

 • day two of the larvae were motionless and apparently dead, three 

 more died on each of the two following days, leaving two nearly 

 motionless larvae, both of which succumbed before noon on January 

 12th. Thus none of the larvae survived more than five days, 

 although under sim..ilar conditions Ransom (1913, p. 14) found the 

 longest period of survival to be between five and eight days. 



F. To determine the period of survival of larval H. muscae in 

 dead flies. 



Twelve flies which '^merged on Decembei- 4th, and died on the 6th, 

 were placed on moist filter paper in a covered Petri dish at noon 

 on the latter date. Twenty-four hours later four were examined, 

 ■two of which contained 13 living larvae, several of which were 



3\ 



