214 
Variability of Ticks 
Porose Areas. 
Independently of the size of the tick, the porose areas may be either 
round, or oval, with the long axis parallel to the median line. When 
the areas are round, the interval between them is about equal to their 
diameter, but when they are oval, the interval is equal, approximately, 
to twice their breadth (dwarf female, Fig. 6). 
Between these two extremes, every stage of gradation may be found. 
Lateral Grooves. 
The lateral grooves are generally obsolete, but occasionally may be 
just visible anteriorly. 
The question as to what comprises a species is very difficult to 
answer. It is a problem which all systematists love to attack, but the 
solution is necessarily influenced by personal bias, species being artificial 
separations tolerated only on account of their utility. 
We have seen that the variability of this species both in size and 
form is very considerable and it is not possible to do more than indicate 
the range found within the species. 
The value of the various structural features, on which the species of 
Rhipicephalus are based, remains to be considered. In both sexes, we 
find in the dwarf forms, structural characters differing considerably from 
those exhibited by the normally developed ticks—for example, the anal 
plates and the form of the palps in the male, and the porose areas in 
the female, each of which is a differential character. If Rhipicephalus 
pulchellus had been an inornate species, the dwarf forms would certainly 
have been considered, even by recent authors, as distinct species. 
Therefore as in all other biological sections great care must be exercised 
in future with regard to species formation, at least within the genera 
of the Brevirostrata, due regard being paid to the probability of an 
apparently new form (differing perhaps from a known species in one 
or two characters only) being but a variant of a known species. From 
this point of view an investigation of the range of the variability, at 
any rate of pathogenic species, would be of considerable value. 
