C. Warburtox 
o 
*) 
that these characteristics are absent in any species unless a large 
number of males had been examined. 
Mere size seems to be of less account in Rhipicephalus than in any 
other genus of the Ixodidae. In the accompanying figures outlines are 
given, drawn to scale, of large and small males of three species, the 
individuals compared being in each case taken from the same tube of 
ticks, collected on the same occasion from a single animal, and connected 
by every grade of intermediate size. The larger specimens usually have 
the specific characteristics (anal plates, punctations etc.) more strongly 
developed than the smaller, and in most species—if not in all—well- 
developed individuals may be found with the body extending beyond 
the scutum and more or less prominent caudally. 
Fig. 1. Outlines of large and small c? ’s of three spp. of Rhipicephalus (from left to right 
R. simus Koch, 1844, R. haemaphysaloides (Supino, 1897) and R. appendiculatus 
Neumann, 1901). Each pair is drawn to scale from specimens taken at the same time 
from a single host. 
It is most unfortunate that the anal plates, which, as highly 
chitinised structures, might be expected to be of great taxonomic 
importance, are subject to very considerable variation, though there is 
generally recognisable a normal form of anal plate for any given species. 
R. lunulatus Neumann, 1907 has such very striking anal plates that no 
one could hesitate, on coming across a single well-marked individual, to 
describe it as a new species. Yet it differs in no other respect from 
R. simus, and we possess specimens taken from a single animal, clearly 
connecting the two forms of anal plate. R. falcatus Neumann, 1908 
presents a similar phenomenon. Indeed the extreme variability of 
R. simus has led to the establishment of several species, some of which 
have already’been suppressed, while others will at least have to be 
degraded into varieties. 
