S. Hadwen 
237 
Conclusions. 
Dermacentor variahilis is a three-host tick and can be raised 
experimentally on rabbits. Starting with an adult female in the spring, 
it is very probable that the life-cycle is carried as far as the nymphal 
moult during the summer and autumn, and that the winter is passed in 
this state, the adults emerging in the spring. Under laboratory con¬ 
ditions about 210 days are required for adults to issue, reckoned from 
the time when the gorged mother tick abandoned the host, without 
taking into account the variable period which the tick may have to 
wait for a host when unfed. 
I am greatly indebted to Mr Norman Criddle, of Treesbank, 
Manitoba, who has furnished me with all the material, and to the 
Veterinary Director-General for permission to publish this article. 
