100 Transactio7is of the Boyal Society of South Africa. 
I am inclined to suspect that stridulation is possible even in this species, 
although it possesses only the first rudiments of the stridulatory organ. 
Passing through the genus, we find a fairly complete gradational series 
connecting those forms in which there is a well-defined granulated stridulatory 
area with those in which the area is prominently ridged and confined to a 
narrow mesial channel. 
It is tempting to suppose that the evolution of the highly developed 
stridulatory apparatus of Parabuthus fiavidus has been guided by some 
process of selection, that in the particular environment occupied by this 
creature the ability to stridulate loudly is of some special advantage. One 
of the results of the hissing of scorpions is without doubt to cause hesitation 
and alarm in an impending foe, but in some species it may also be a sexual 
call. In such forms as P. laevifrons militum, and probably also in P. stridulus, 
the development of the cross ridges of the stridulatory apparatus is much 
more strongly pronounced in males than in females, though in other respects 
the male is not more powerfully developed. Still, in various genera of 
scorpions the granularity of any particular region is often much more 
strongly marked in males than in females ; this is the case, for example, in 
various species of Opisthacanthus in respect to the sides of the fifth caudal 
segment and the lower surface of the vesicle, and it also applies very 
markedly to the granulation of the sternites in the genus Opisthophthalmus. 
In such cases it is by no means clear that the secondary sexual differences 
are the result of some form of sexual selection. 
In the genus Opisthophthalmus the variation of the stridulatory 
mechanism is of a different type, and no sexual differences are known in 
this character. The stridulatory lamellae are either completely absent or 
present in a fully developed condition, the number varying from 1 to 7. 
Seeing that a stridulatory apparatus has been developed amongst our 
scorpions in three quite different ways, we may assume that the function 
must be of considerable importance ; yet, in the genus Opisthophthalmus, 
species which do not stridulate may enjoy a wide distribution and sometimes 
occur with equal abundance in the same localities as their closely related 
allies which do stridulate. 
Key to the Families and Subfamilies of South African Scor]jions. 
1. Arising from the articular membrane between the tarsus and pro- 
tarsus * of each leg, there is inferiorly a pair of pale but dark-tipped claw- 
like spurs, the anterior one of which is usually double ; and between the 
protarsus and tibia of the third and fourth legs there is a single spur 
* Pocock's nomenclature of the segments of the legs and pedipalps is here 
followed, viz. : in the leg. Coxa, trochanter, femur, patella, tibia, protarsus, and 
tarsus; in the pedipalp. Coxa, trochanter, humerus, brachium, hand, and movable 
finger. 
'J 
