302 



Genus Ixodes 



last 1^ to 2 years. It seems, however, possible that a whole generation 

 may be evolved in one season under very favourable conditions. 



Allowing only ten days for a tick in the larval and pupal stages in 

 which to harden after metamorphosis and to find a host, and 11 weeks 

 for metamorphosis thereafter, Wheler calculates the time occupied as 

 follows : 



Larva ... 

 Nymph 

 Adult ? 



13 weeks (l£ free, \ on host, 11 gorged). 

 13 „ (1J „ i „ 11 „ ). 

 H m (1* „ 2 „ 4 „ ). 



In one case the larvae fasted 40 weeks, and allowing 11 weeks for 

 metamorphosis after an assumed feeding, practically a whole year would 

 be accounted for. According to Kossel and his colleagues (1903, p. 43) 

 it takes at least five months for a generation to develop ; our estimate, 

 based on the following figures, gives the shortest period at about six 

 months. 



On the basis of the observations here recorded, I would calculate 

 the time it takes for a generation to develop on a warm-blooded host 

 as follows : 



Fecundated ? abandons the host. 



¥ begins to oviposit after 



Larvae hatch out from the eggs after 



Larvae harden and wait to attack host No. 1 

 after 



Larvae remain upon the host for 



(Larvae, having abandoned the host, undergo 

 metamorphosis.) 



Nymphs issue from the larval skin after ... 



Nymphs harden and wait to attack host 

 No. 2 after 



Nymphs remain upon the host for 



(Nj mphs, having abandoned the host, under- 

 go metamorphosis.) 



Adults issue from the nymphal skin after 



Adults harden and wait to attack host No. 3 

 after 



Adults ( ? s) remain upon the host for ... 



Fecundated ? abandons the host 



About 170 days probably represents the shortest possible time 

 required for the completion of the life-cycle, if we deduct a few days 

 from the usual time which appears to be necessary for hardening after 



28 



84-140 



