204 
THE VARIABILITY OF RHIPICEPHALUS 
PULCIIELLUS (GERSTACKER, 1873), 
TOGETHER WITH ITS GEOGRAPHICAL DISTRIBUTION. 
By NORMAN CUNLIFFE, B.A., 
Student in Medical Entomology. 
{From the Quick Laboratory, Cambridge.) 
(With 6 Text-figures.) 
It has been pointed out by Warburton (1912) that the degree of 
variation within the species of the genus Rhipicephalus is very consider¬ 
able, and in view of this fact it is important to investigate the range of 
a species and the value of the diffei’ential structural characters upon 
which species are based. The great majority of the Rhipicephali are 
inornate and this, in conjunction with the general lack of distinguishing- 
structural features and the wide variation found within the species, 
renders determinations difficult. As Rhipicephalus pulchellus, however, 
possesses a characteristic and Avell-marked ornamentation, which is 
subject to but slight variation, any specimen, at least in the case of the 
males, may be determined without difficulty. 
Hence this species is invaluable for such an inquiry, and as a casual 
observation of a number of specimens obtained from one host showed 
a great range in size, Prof. Nuttall suggested that I should examine 
critically a number of individuals collected under natural conditions. 
The material available for observation in Cambridge has been collected 
in Africa during a period of nine years. Of each consignment received, it 
has been customary to return a number of specimens after determination 
and to retain the largest and smallest individuals. Thus it is probable 
that the naturally-occurring extremes have now been received. The 
retention of the extremes applies more particularly to the males, in 
which the valuation in size of the scutum is more noticeable than in the 
females. This artificial selection and the limitation of the number of 
