212 Variability of Ticks 
glabrous surface. The spiracle shows no important modification, but 
the general chitinisation is less strong in the dwarfs, except for the 
coxal armature and the auriculae of the basis capituli, and for this reason 
such organs as the spiracles and the anal plates are not raised above 
the general surface. 
Female Scutum. 
The variation in the structural features of the females of Rhipi- 
cephalus pulchellus is practically negligible, the dwarf specimens being 
smaller replicas of the larger forms. The ornamentation of the scutum, 
the cervical and lateral grooves, the punctation, the shape of the basis, 
the spiracle, and lastly the hairs and depressions of the dorsum, in fact 
almost all the characters by which a species determination is made, are 
3 5 6 8 17 11 2 1 0 
Fig. 5. Correlation diagram, female. 
remarkably constant, except of course in size. The following table gives 
the extreme and average dimensions of the female scutum : 
Length in mm 
Largest specimen 2-2 
Smallest specimen 1'5 
Average specimen 1*9 
In the majority of cases, however, the scutum is either slightly longer 
than broad or vice versa, as is shown by the spreading on each side of 
the diagonal in the correlation diagram (Fig. 5). Here also the correla¬ 
tion coefficient is high, being 0 - 95. 
Breadth in mm. 
2-2 
1*5 
1*9 
