98 
Transactions of the Jttoyal Society of South Africa. 
the Eastern species JJ.formosus, which is very common in Natal and Eastern 
■Cape Colony, apparently extends westwards only as far as Port Elizabeth. 
Such facts find numerous almost exact parallels in the distribution of 
various groups of animals and of plants in South Africa. 
Now if these areas are, as I believe, characterised by distinct environ- 
mental conditions, we may infer that directly or indirectly the diversity of 
environment afforded within the whole region has probably been an important 
factor in the causation of the diversity now found within a genus. How this 
factor has operated we do not know, nor does it seem necessary to suppose 
that all species formation is connected with environmental differences. 
There are systematists who claim that a direct connection can be estab- 
lished between the multiplicity of species in a genus and diversity of en- 
vironmental conditions. For instance, a generalisation of plant distribution 
known as Jaccard's Law states that " the generic coefficient is inversely 
proportional to the diversity of ecologic conditions" — the generic coefficient 
„ ^ ^ . . , . total number of genera 
01 a nora being the traction , , . r s ^- expressed tor convenience 
^ total num ber oi species ^ 
as a percentage. Unfortunately, in the case of scorpions we can form no 
proper estimate of the value of this proj)Osition owing to our ignorance of the 
important ecological conditions. Even when two allied species occur side by 
side, as they sometimes do, it is still just possible that each may be exactly 
correlated with some special minutiae of the environment. In a general 
way we can say that amongst the external factors which matter to scorpions 
are — degree of humidity, nature of the surface of the ground (especially in 
the presence or absence of large stones), nature of the soil, and probably the 
minimum winter temperature ; but, having ascertained such data in the 
several portions of any particular region, no one would venture to predict 
what the generic index may be. This so-called law is in fact only a plausible 
hypothesis, as yet not adequately supported by actual facts. Although, as I 
have previously stated, the environmental factor is probably an important one 
in species formation, yet in several regions which are particularly rich in 
species this is apparently not the sole factor of importance : it is doubtful if 
the exceptional richness in species of Opisthophthalmus and Parabuthus that 
characterises the arid regions of North-West Cape Province can be rightly 
connected with a corresponding diversity of environmental conditions in that 
region. So far as we know at present, mere isolation may be the cause of 
considerable diversity, at least within a species : as in many other sluggish 
creatures, local forms are very numerous, and without doubt are an indirect 
result of isolation, though how far other factors may have co-operated we 
cannot say. 
So far as I can judge, structural adaptations to particular environments 
are not strikingly exhibited. The coarse granulation of the sternites and 
of the lower surfaces of the anterior caudal segments in various species of 
