34 Gerald F. Hill: 



D. To dtiteiinine the period of survival of larvae removed from 



tlies. 



During the afternoon of January 16th, 25 H. microstoiiia larvae 

 from the heads of tAVo Stomoxys flies were placed in normal saline 

 contained in a small covered Petri-dish and examined daily until 

 Januai'y 20th. Two were dead on Januaiy 17th, five on January 

 18th, twelve on January 19th, four on January 20th, leaving two 

 living at noon on the last date. No examination was made on 

 January 21st, but both were found dead early on January 22nd. 



E. To determine the period of survival of larvae in dead flies. 



A Stomoxys fly Avhich emerged on January 14th was kept in a 

 wire-gauze cage until January 16th, when it died. It was then 

 placed on moistened paper in a covered Petri-dish, where it re- 

 mained for forty-eight hours. On dissection the head and the 

 proboscis were found to contain 35 dead larvae. 



F. To determine the possibility of escape of larval H. micros- 



toma from flies. 



Stomoxys flies were frequently placed in moist, and, in dry, tubes 

 for periods up to thirty hours, to determine whether under such 

 -conditions the parasite would escape either before or after the 

 •death of insects. Although the flies were subsequently proved to 

 be heavily infected, in no instance were parasites found free in the 

 tubes. 



Time has not permitted, so far, of much experimental work to 

 determine whether or not larval H. microstoma may be carried 

 into a wound made by a Stomoxys fly during feeding operation, 

 but on January 12th attempts were made to induce Stomoxys flies 

 {afterwards pioved infected) to bite horses by placing them on 

 various parts of the skin, including a bare patch on the back. In 

 some cases there was a determined attempt on the part of the flies 

 to bite, but strangely enO'Ugh none succeeded in penetrating the 

 skin. Two of these experimental flies were subsequently dissected 

 and found to harbour 1^ and 15 parasites respectively in the pro- 

 boscis and 14 and 25 respectively in other parts of the head. 



The escape of larvae from freshly severed heads in normal saline 

 has been observed frequently. The exit of the parasite is made 

 very rapidly, either from the tip of the proboscis, or by forcing its 

 Avay out between tlie lal>ium and the labrum.-epipharynx. Photo- 



