GEOGRAPHICAL DISTRIBUTION. 91 
have also published studies made of that species. Capt. S. R. 
Christophers, working in India, has studied Rhipicephalus sanguineus 
(1907) and made observations on Ornithodoros savignyi (1906). 
In South America, Dr. F. Lahille, of Argentina (1905), has studied 
Margaropus annulatus australis and Dr. C. J. Rohr, of Brazil (1909), 
has conducted extensive investigations on six species. Newstead 
reported in 1909 on studies made in Jamaica. Among others who 
have studied the cattle tick are Ransom (1906), Newell and Dough- 
erty (1906), Schroeder (1907), Hunter and Hooker (1907), Cary (1908), 
Cotton (1908), and Graybill (1911). Many others have recorded mis- 
cellaneous observations on different species. Preliminary notes on 
several species were published by Hunter and Hooker in 1907, and 
further information has since been published by Hooker (1908, 
1909a, b,c). 
GEOGRAPHICAL DISTRIBUTION. 
The ticks that commonly attach to the domestic animals have been 
widely disseminated on the hosts so that now many of them are only 
limited by climatic zones. Of the several meteorologic factors 
which control their distribution cold appears to be the most impor- 
tant, although excessive heat and variation in humidity are also 
important. Thus in America we find the tick species most abundant 
in the Tropical and Lower Austral zones and the least so in the 
Boreal Zone. Several native species, notably Margaropus annulatus, 
Amblyomma maculatum, and Argas miniatus rarely appear above 
the Lower Austral Zone, while Amblyomma tuberculatum, A. dissimile, 
A. cajennense, and Dermacentor nitens occur only in the Tropical or Gulf 
strips of the Lower Austral Zone. Our two species of Ceratixodes, 
namely, putus and signatus, apparently occur in the Boreal Zone only. 
Some species remain attached to their hosts for long periods (par- 
- ticularly the males) and may be carried great distances. This has 
resulted in numerous records which must be rejected in determining 
the normal distribution of a species. The approximate zonal dis- 
tribution of our species is shown in Table I. 
