96 Gerald F. Hill : 



From an analysis of these experiments it will be seen that the 

 most favourable condition and location for the survival of the- 

 adult parasite off the host was a piece of tree trunk resting on sheep- 

 pen sweepings in the cellar in winter; the next most favourable con- 

 dition was an open jar of sheep-pen sweepings in a sheep shelter 

 in spring; the next was the lawn grass in the cellar, soil with leaves- 

 on the surface in cellar, and soil without leaves on the surface ia 

 cellar, in all three of which the parasites lived equally long. The 

 most favourable condition w^as the tree trunk on sheep-pen e\N^eep- 

 ings on the lawn, where the "ticks" lived eleven days in winter 

 and six days in spring; the next bare soil on the lawn, soil with, 

 leaves on the surface, and sheep-pen sweepings in a sheep-shelter, 

 in all three of which the insects died in ten days during the winter. 

 The next most favourable condition was the sod of lawn grass on. 

 lawn in winter, and the natural surface of the sheep-yard in winter^ 

 where the parasite lived nine days. Under the latter condition in 

 spring, two groups of " ticks " all died in five days. Finally, the- 

 least favourable condition was the sheep's wool on the laboratory 

 table and in the cellar, where the insects Avere all dead in two days. 



Influence of age and condition on viahility . — It Avill be seen from 

 the above summary that generally the adult possesses greater 

 vitality than either young fed ''ticks," from three to seven days- 

 old, or young unfed "' ticks," under one day old, and that " ticks " 

 between three and seven days old possess greater vitality than those 

 under one day old. Swingle, as has been stated, found that young 

 '' ticks " before taking a meal could be kept alive off the host a little 

 longer than adults. In twelve experiments carried out by the- 

 present writer adults outlived unfed ''ticks" under one day old;. 

 in one experiment the latter outlived the former and in one experi- 

 ment both classes lived equally long. In ten experiments adults 

 outlived young " ticks " about seven days old; in one experiment 

 the latter outlived the former, and in one experiment they lived for 

 an equally long period. In nine experiments young fed " ticks " 

 between three and seven days old outlived young unfed " ticks" of 

 less than one day old; in two experiments the latter outlived the 

 former, and in one experiment both closses lived for an equally long 

 period. 



Influence of sex on viahility. — These experiments show that female 

 " ticks " are possess^ed of greater vitality than males. Both sexes 

 were used simultaneously in forty-two experiments, and in twenty- 

 seven of them the females survived longer than the males. In four 

 experiments the males outlived the females and in eleven experi- 



