106 Gerald F. Hill: 



days, which is the longest period for which these classes have been 

 kept. 



Under more natural out-of-door conditions the maximum time of 

 survival was, for adult ''ticks," eleven days, for three to seven 

 days old (fed) '* ticks " ten days, and for one day old (unfed) 

 *' ticks " eight days, on a small part of a tree-trunk with loose 

 bark on a sheltered lawn, and ten, eight, and seven days respec- 

 tively when on surface of soil on same lawn, though in each case- 

 the majority of the "ticks" died before the end of the fourth or 

 fifth days. 



Excepting under the influence of extremes of temperature, a 

 certain proportion of the pupae are viable for varying periods uj> 

 to forty-tAvo days after removal from the host. 



The percentage of pupae which retain their viability off the host 

 varies very greatly with the influence of temperature. When pupae- 

 were placed on moist sheep-pen sweepings and incubated at tempera- 

 tures varying from 64.4°F. to 82.4°F., 100% produced young- 

 Louse-flies between tlie tenth and twenty-sixth day. Under more 

 natural conditions, the percentage was found to be lower, for 

 example, pupae which were placed in a small quantity of wool on a 

 fence post out of doors, where the temperature varied from 47 °F. to- 

 84°F., produced 31.5% of young flies between the third and twenty- 

 seventh day. On sand out of doors, two groups of pupae produced 

 only 6% of young flies. In all other out-of-door experiments, pupae^ 

 failed to develop when removed from the host. 



The experiments and observations recorded in the preceding 

 pages show that there is some slight ground for the contentions of 

 those sheep-owners who maintain that sheep previously freed of 

 Louse-flies by dipping may become reinfec-ted with other " ticks "" 

 which have been left on grass, bushes or posts, etc., or with young 

 " ticks " which liave emerged from pupae dislodged from the fleeces 

 of infected sheep. The present writer, however, cannot find any 

 record of Louse-flies or their pupae having been found under such 

 circumstances, though tlie transference of the adult insects from 

 the fleece to bushes, posts, logs, etc., appears to be extremely prob- 

 able in view of the habit of these insects in coming to the surface of 

 the fleece in Avarm weather. It is quite conceivable also that a few 

 pupae are dislod52:ed whilst the host is engaged rubbing against 

 fence-posts, branches, etc. 



Possibly other pupae fall from the fleece to the ground as a result 

 of the dipping fluid or heavy rain dissolving the glutinous matter 



