[57] Adaptation of Ticks 335 



In the appended lists I have grouped the various species of Ixodes 

 as follows : 



I. Species of which both the </" 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. 



II. 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. 



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 Cants 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 occurring upon wandering hosts. 



Group 1 (b). 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 1 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. 



