F. C. Bishopp and H. P. Wood 
171 
to attain a thickness of 1'9 mm. The thickness decreases somewhat as 
the development of the adult within the nymphal skin progresses. 
The shortest period between the moulting of larvae and moulting of 
nymphs noted by us was six days. We are inclined to think that some 
nymphs began moulting a day or more before being observed in the 
two cases where the duration of the nymphal stage was six days. The 
usual period, from the moulting of larvae to the moulting of nymphs, 
appears to be 9-12 days (see Table VI). 
Nymphs, which moulted from larvae detached from a host, attached 
themselves again when given an opportunity. Several nymphs which 
had moulted off a host were put on an ox on January 24, 1910. About 
half of these died without becoming attached while the others became 
attached, and on February 1 one fully engorged specimen was found 
detached. Another was detached on February 9 and a third on 
February 14. The last individual remained on the host until March 4 
when it was found detached and apparently fully engorged. In this 
instance the last nymph had been on the host for 39 days. In another 
case a nymph put on an ox March 11, 1910, was fully engorged on 
March 23. 
As previously mentioned, the nymphs are easily detached, especially 
when engorged, and this often happens in nature. Although some of 
them are held on the host by the long winter coat of the animal, many 
undoubtedly fall to the ground and moult to adults, some of which 
again find hosts. Table Y shows the range in the moulting period of 
nymphs detached from the host and kept upon moist sand in the lab¬ 
oratory at Dallas, Texas. In this case, as in the moulting of the larvae, 
the temperature and state of development of the ticks at the time of 
detachment are the most important factors governing the moulting 
period. Nymphs approximately one-half engorged, have been found to 
moult when removed from a host, but individuals less than one-half 
engorged invariably die. 
The Adult (PI. X, figs. 5, 6 ; PI. XI, figs. 1-6): Since this species 
normally remains on the host to moult, the longevity of unattached 
adults is of much less practical importance than it is with species which 
drop off their host before moulting. However, engorged nymphs, as 
well as adults, are often detached by the host. We have found also 
that adults will reattach themselves to hosts even though they are one- 
fifth engorged. These facts increase the importance of a knowledge of 
the longevity of adults moulted from nymphs previously removed from 
a host, as well as the longevity of specimens detached in the adult 
12—2 
