80 Gerald F. Hill : 



the nineteenth day, five on the twentieth day, and two on the- 

 twonty-first day. The remaining pupa was infertile. The area of 

 wool, 2 in. in diameter, was enclosed in a metal ring 3 in. in 

 diameter and 1 in. deep, secured to the skin with pitch plaster. 

 The wool was J in. long and the pupae were laid by the females- 

 about the middle of the staple. The stall used was the one referred 

 to above, and in it the temperature ranged from 47°F. to 72°F.. 

 during the experiment. 



Summary and Observations. 



The incubation period of the pupa on the host has been found 

 to be twenty-two to twenty-four days during the winter months. 

 May and June, when the temperature varied between 43°F, and 

 47°F. and nineteen to twenty-one days during the spring months,. 

 September and October, when the temperature ranged from 47°F. 

 to 72°F. 



Swingle found in U.S.A. that the incubation period of the pupa 

 on a sheep kept in a barn was twenty to thirty-six days in winter, 

 when the average minimum temperature was 7.2°F. and the average 

 maximum temperature 27.3°F. In summer, when the average 

 minimum temperature was 44°F. and the average maximum tem- 

 perature 74°F., the period was nineteen tO' twenty-three days. He 

 considered that were the sheep turned out of doors in winter, the 

 period might be increased tO' forty or forty-five days in some cases. 



2. To determine the period required by the young Louse-fly to 

 reach maturity, i.e., the period elapsing between its 

 emergence and the extrusion of the first pupa. 



Experiment No. 3. 



On May 21st one male and eight female " ticks " which emerged 

 from their pupae on the previous day were placed in a small area 

 of Avool on a sheep's back. The temperature in the sheep-pen, 

 which was similar to the one referred to on page 79, ranged from 

 44"F. to 66°F. during the experiment. Tlie wool was about f in. 

 long and the enclosed space about 2 J in. in diameter. The sur- 

 rounding wool was closely shorn to allow a clear space of six inches 

 around the 2 J in. circle of standing wool. Vaseline was then smeared 

 freely on the shorn portion with the object of preventing the young 

 *^ ticks " escaping. On the following day (May 22nd), several adult 

 " ticks " from other parts of the host were found in the area under 



