16 LIFE HISTORY OF NORTH AMERICAN TICKS. 
States, by Mr. Nathan Banks, a work became available by means of 
which most of the ticks of this country can be readily identified. 
Since this work appeared several new species have been described 
by Messrs. Banks (1910), Stiles (1910), and Bishopp (1911b),?so that at 
present 42 species and 3 varieties representing the genera Argas, 
Ornithodoros, Amblyomma, Aponomma, Ceratixodes, Dermacentor, 
Hemaphysalis, Ixodes, Margaropus, and Rhipicephalus, are known 
to occur within our borders. A valuable monograph of the Ixodoidea 
is being published by Nuttall, Warburton, Cooper, and Robinson. 
Two parts, dealing with the Argasidae, the classification of ticks, and 
the genus Ixodes, have been issued. 
A detailed illustrated account of the general structure of ticks, to 
which reference should be made, has been given by Salmon and Stiles 
(1901, pp. 387-398). It may be well, however, to give a brief descrip- 
tion of the so-called capitulum or head, bearing the palpi and the 
haustellum, the latter of which consists of the mandibles, mandibular 
sheaths, and hypostome, which are inserted into the skin of the host. 
The capitulum is a small subtriangular piece that articulates with 
the anterior margin and usually within a slight emargination of the 
corneous shield, or scutum, which in the ixodid female forms the 
front part of the dorsum and in the male covers the greater part of 
the body. The hypostome, or labium, which lies underneath the 
mandibles, is an elongated dart or spatulate structure, which is com- 
posed of 2 lateral symmetrical halves bearing many hooks or denticles 
directed backward, so that when embedded in the flesh it can not be 
forcibly withdrawn with ease. The mandibles, 2 in number, are 
terminated anteriorly by either 2 or 3 processes, known as apophyses, 
that are used for piercing the flesh and making an entrance. The 
mandibular sheaths surround the base of the mandibles and extend 
backward on the dorsal side of the haustellum. Upon each side of 
the haustellum, applied closely thereto, are the palpi, which are 
grooved on the inner margin. 
There is considerable variation in the size of the individual ticks 
of a single species, among both males and females. The engorged 
nymphs also vary in size, the larger usually being prefemales.? Under 
the several species measurements will be found which indicate the 
variation. The color, especially of the immature stages, is also quite 
variable. In engorged larve and nymphs of some species there is a 
variation from dark brown to pink and pale gray. This is apparently 
1 For the classification of the ticks the worker is referred to Mr. Banks’s Revision of the Ixodoidea (1908). 
Descriptions of adults, aside from their size and coloration, have been omitted in the present work, as they 
will be found in Mr. Banks’s Revision. 
2 See Bibliographical references, p. 205. 
3 The terms ‘‘premale” and “‘prefemale” have been used to denote those individuals, not yet molted to 
adults, in which the sew can be recognized, 
