46 
ON THE ADAPTATION OF TICKS TO 
THE HABITS OF THEIR HOSTS i. 
By GEORGE H. F. NUTTALL, F.R.S. 
{From the Quick Laboratory, University of Cambridge.) 
(With 26 Text-Figures.) 
In the course of the extended investigation upon ticks which we 
have been conducting for some years, a very large number of specimens 
have reached us from all parts of the world, thanks to the generous 
aid which we have received from numerous collectors. In addition to 
studying this material, the literature on ticks has been sifted for any 
information which might throw light upon these parasites. A study of 
the data relating to the structure and habits of ticks and of their host 
relationships has brought to light certain facts which possess consider¬ 
able interest and consequently appear to me worth recording in this 
Journal. 
The superfamily Ixodoidea is divided into two families, the Argasidae 
and Ixodidae, which are distinguished from each other by their external 
structure as well as by their habits^ 
General considerations regarding the Biology of the Argasidae 
and Ixodidae. 
The Argasidae are mostly inhabitants of warm climates. When 
they occur in colder parts of the world they seek hosts whose habitats 
atford them protection, and insure them possibly a certain degree of 
' Bead before the Cambridge Philosophical Society Meeting, 20 February, 1911. 
2 The main structural differences are described by Nuttall and "Warburton (1908) in 
Ticks; a Monograph of the Ixodoidea, by Nuttall, Warburton, Cooper and Eobinson, 
Part I, p. 1. 
