80 
Biologu of Ixodidae 
regard to the time the tick remains upon the host during its different 
stages. It is clear, however, that it seeks a host three times, i.e. as 
a larva, nymph and adult female. 
From the foregoing data regarding the time required for meta¬ 
morphosis we may conclude that the larva developes in 84-129 days 
at an average temperature of 12° C.; eight lots of larvae emerged after 
84-90 days, six after 93-99 days, six after 101-129 days. The data 
regarding the later stages do not permit of definite conclusions because 
the gorged larvae and nymphs were doubtless in a more or less advanced 
stage of metamorphosis when they were captured. Most of them were 
however quite lively, behaving like ticks which had but recently 
abandoned the host. It is possible therefore, if we take the longest 
periods observed, that metamorphosis from larva to nymph may take 
place in 17 days or more and that the nymph developes into an adult 
in 39 days or more. In the protocols dealing with the longevity of 
unfed adults (p. 84) I have noted the time required by each tick to 
undergo metamorphosis. It is worth mentioning that the males appear 
to require more time for metamorphosis than do the females, thus 
the longest periods noted for three males were 30, 34 and 39 days 
respectively, whereas the corresponding periods for three females were 
19, 22 and 22 days respectively. That males may take longer than 
females to develope from gorged nymphs is rendered still more probable 
by the difference in size which I have noted between the gorged 
nymphs which give rise to males and females respectively. 
Male and female nymphs. 
Except by examining the internal organs, it has hitherto been found 
impossible to distinguish the sexes in the nymphs of Ixodidae. Having 
become convinced that the males of certain species of Ixodes do not feed 
upon the host {I. hexagonus, caledonicus, canisuga, putus, etc.) I sought to 
discover if any differences could be detected between the sexes in the 
nymphal stages. Arguing, that if the male has to store up all the 
energy required for its sexual life prior to emerging as an adult 
I concluded that there might be a difference observable in the size 
of the nymphs whence the males and females emerge. According to 
this view the male nymphs should be larger than the females because 
the male would store more food than the female in the nymphal stage. 
Having 22 gorged nymphs of I. putus at my disposal last year, 
I rapidly separated them into two lots; 11 large ones and 11 small or 
