ADAPTATIONS. 27 
To this class belong several other species which have partially over- 
come this disadvantage by passing the first molt upon the host. Two 
representatives of this class are the South African species Rhipice- 
phalus bursa and R. evertsi. It has been overcome entirely by Orni- 
thodoros megnini, the spinose ear tick, in a somewhat different way— 
that is, by passing the first molt upon the host, then feeding suffi- 
ciently as a nymph so that following the second molt, which takes 
place off the host, engorgement as an adult is unnecessary for oviposi- 
tion and probably never occurs. 
Even in species most diverse in their tastes there are hosts espe- 
cially favored. This in some cases may be accounted for by the great 
numbers of that host available. In the class which has adapted its 
habits to the habits of the host, the ticks are confined largely to a 
host or group of hosts with similar habits. The species Hemaphy- 
salis leporis-palustris, commonly known as the rabbit tick, has adapted 
itself to the habits of the Leporide, the hares and rabbits, and only 
accidentally attaches to other hosts. It is the habit of the hares and 
rabbits to remain more or less inactive during the day in their “forms,”’ 
or resting places, protected by a clump of grass or bushes from ene- 
mies, such as birds of prey, their activity being largely at night. 
The writers have found that this tick following engorgement drops 
largely during the day; in other words, when the hares and rabbits 
are in their forms or resting places, to which they return to pass the 
day. Thus, when the ticks have hatched or molted and are ready 
to attach, they have little trouble in finding the host. This same 
habit has been acquired by the fowl tick, Argas mimiatus, which, in 
the engorged larval stage, the writers find, drops only at night 
(except accidentally), when its host, the fowl, is upon the roost. 
Thus when ready to reattach it is near and readily finds the host, 
whereas had it dropped during the day when the fowl was on the 
“run’”’ the chances of its finding a host would be greatly lessened. 
A habit apparently acquired by Ornithodoros megnini is that of 
crawling to a height of several feet from the ground as a nymph 
before molting and depositing its eggs; thus when the seed ticks 
appear ready to attach they will be rubbed off by the horses, cows, 
or other host, and readily find access to the ear. The extreme agility 
of the unengorged adults of Dermacentor parumapertus marginatus 
and Rhipicephalus sanguineus undoubtedly greatly aids these spe- 
cies in finding a host and in finding a place of attachment before 
being dislodged by the host. These species furnish what evidence 
we now have of the adaptation of habits to the habits of the host, 
but it seems probable that similar habits will be discovered in other 
species when they have been given sufficient study. 
Dr. Nuttall has recently (1911a) discussed a structural adaptation 
which he believes to have resulted from the interrelationship of 
