C. Warburton 
0 
confused, and that the species were in fact numerous, though difficult of 
separation. But it is strongly supported by the results obtained by the 
I'earing of ticks in the laboratory, and this has been done over and over 
again in the case of common species such as R. appencUculatiis and 
R. capensis. The wide divergence of individuals raised from a single 
batch of eggs is most striking, especially as regards the males. The 
disparity in size of captured male ticks apparently belonging to the 
same species was often so great as to suggest that the males lived 
longer than was supposed and grew after reaching maturity ; especially 
as the larger specimens were almost always more highly chitinised and 
more strongly characterised, but similar differences are observed in 
newly emerged males which have been reared in the laboratory from 
nymphs taken from one host. 
The genus Rhipicephalus is essentially African. R. sanguineus is 
practically cosmopolitan—a fact no doubt attributable to its usual host, 
the dog. R. bursa has overflowed into southern Europe, being chiefly 
distributed along the shores of the Mediterranean. R. texanus Banks, 
1908 is certainly no more than a N. American variety of R. sanguineus, 
if it deserves even varietal rank, and the only known distinct Asiatic 
Rhipicephalus seems to be R. haemaphysaloides. 
Now the writer has, during the last few years, examined many 
thousands of ticks collected from all parts of Africa, chiefly in connection 
with the work of the Entomological Research Committee. He has also, 
thanks to the great courtesy of various collectors and of the authorities 
of the chief continental museums, been able to study the actual types 
of nearly every so-called species of Rhipicephalus, and his conclusions, 
as far as he has been able to arrive at any, will, it is hoped, be of some 
interest to those who have to deal with this most puzzling group. 
The first conclusion is that the genus Rhipicephalus is in an 
extremely fluid condition. There are what appear to be a considerable 
number of species in the making —forms distinct enough when charac¬ 
teristic examples are selected, but in many cases merging into each 
other by imperceptible gradations. 
A certain number of forms—about sixteen—have been repeatedly met 
with in considerable numbers, and though they often include ill-charac¬ 
terised individuals, they each centre round a recognisable type distinct in 
each case. In the second place there ai’e certain forms {e.g. R. armatus 
Pocock, 1900, R. cuspidatus Neumann, 1906, R. deltoideus Neumann, 
1910) of which few examples have ever been found, but which are so 
peculiar that their claim to specific rank cannot be denied. Lastly there 
