72 Biology of Ixodidae 
but seek the females in the hosts’ burrows or nests where the females 
drop off gorged and the males undergo their metamorphosis from 
nymphs. 
(3) The time required for metamorphosis from stage to stage ; egg 
to larva, larva to nymph, nymph to adult, under varying conditions of 
temperature, etc. 
(4) Oviposition : the time which elapses before the female begins to 
oviposit; the time required for oviposition; the number of eggs laid by 
single females. 
(5) Longevity of the larvae, nymphs and adults when maintained 
unfed under stated conditions of temperature and moisture. 
(6) Part fayed in pathology if ascertainable : in the transmission 
of disease and through the effects of their bites. 
I am fully aware that some of my records are deficient in certain 
particulars; it has been found impossible for instance to raise certain 
species under experimental conditions. With regard to copulation the 
process has been observed in Argas, Ornithodorus and Ixodes, but not to 
my knowledge in any other genus. From the data comprised under 
some of the above headings, however, it will be possible to conclude how 
long a given species will take to complete its life cycle, beginning say on 
the day when the first eggs of a generation are laid to the day when the 
first eggs of the second generation appear. 
That observations in the laboratory require to be supplemented by 
others carried on in the field is self-evident. Field observations are, 
however, not readily carried out except in tick-infested countries. 
A fallacy which may arise from laboratory experience alone concerns 
for instance the supposed length of time required for the completion of 
the life cycle. We know that ticks have great powers of fasting in the 
absence of a host and that they may hibernate. The time required for 
the completion of the life cycle may therefore vary considerably and be 
much prolonged under unfavourable conditions. In the summary at the 
end of the sections dealing with each species mentioned in this paper, I 
have given the time which the species requires to complete its life cycle 
under the favourable conditions of laboratory experiment. In nature, 
no doubt, this period is in the majority of instances more or less con¬ 
siderably prolonged. 
In the course of our raising experiments, we have noticed that the 
records of “the time the ticks remain upon the host” are open to a 
certain fallacy in that some ticks do not immediately proceed to feed 
upon the host; this holds more particularly for what we have observed 
