G. H. F. Nuttall 57 
In the appended lists I have grouped tlie various species of Ixodes 
as follows: 
I. Species of which both the cT and $ are recorded as occurring 
upon the host. 
(a) Species in which the sexes have been found in copula upon 
the host. 
(b) Species in which the sexes have been found near together 
upon the host. 
IL Species of which the females only have been found upon the 
host. 
III. Species of which the females only are known. 
The immature stages of these ticks are left out of consideration in 
these lists. Alongside the name of the hosts are placed certain signs: 
+ denotes a host possessing wandering habits. 
0 denotes a host with fixed habitat for more or less prolonged 
periods; the habitats being burrows, nests, caves, hollow trees, etc. 
+ is used in the case of Canis familiaris, as in some places it may 
be fittingly described as a wandering host, in others as a host with fixed 
habitat (the kennel). 
A consideration of the data tabulated in the following pages brings 
out certain striking facts. The ticks included under Group 1 (a) are, in 
most cases, encountered upon (+) wandering hosts. In the case of 
ricinus, our records show that it has been found 63 times on wandering 
hosts and only 10 times on hosts which burrow. Being a very pre¬ 
valent and hardy species, it is natural that it should occasionally occur 
on a variety of hosts. The tick may at times infest dog kennels, thus 
taking advantage of the fixed habitat of the host. The three varieties 
of ricinus (var. scapularis, ovatus and californicus) appear to follow the 
same rule, and in the case of pilosus we appear to have a striking 
example of a tick occuri’ing upon wandering hosts. 
Group 1 (6). The species included in this group occur, in some cases, 
on wandering hosts, in others not. Thus, angustus and tenuirostris, ac¬ 
cording to my notes, occur solely on nesting and burrowing animals. In 
angustus we have a form in which the males occur very rarely upon the 
host, and in which the male hypostome^ is poorly armed; angustus may, 
therefore, be regarded as an intermediate form in respect to its adapta¬ 
tion. In tenuirostris we have a tick which, as far as we know, only 
1 The variations in this structure in male Ixodes will be discussed presently. 
