Contributions to a Knoivledge of South African Oligocliaeta — Part I. 239 
These remarks may be construed as signifying one of two 
conclusions : — 
{a) The Hving PhreodriUdae are the descendants of an old cold climate 
ancestral stock which once inhabited the southern lands, and are now 
restricted to areas where these conditions are now attained ; or — 
{h) The Phreodrilidae are the remnants of a stock which has been 
unable to meet the demands for existence under normal and temperate 
conditions, and consequently have taken up an abode in places w^here the 
struggle for existence is far less keen. 
Before discussing these conclusions we will mention several facts 
which wall tend to make the issue more easily understood. 
Firstly, the Phreodrilidae undoubtedly show marked affinities, when 
phylogenetically considered, with the Lumbriculidae, and the latter are as 
truly restricted to the Northern, as the former to the Southern 
Hemisphere , 
Secondly, it would appear that the Phreodrilidae are not capable of 
transmigration across sea barriers, as are so many of the terrestrial 
Oligocliaeta. They do not meet with the same chances of migration at 
the hands of man like many terrestrial Oligocliaeta — a fact which is 
explained by their habitat, and that the chief medium serving for 
conveyance in the hands of man is either soil or water ; and which is 
supported by the absence of Phreodrilidae except in the restricted habitats 
mentioned above, and by the fact that as yet no species is known as being 
common to any two of the land areas where the family is represented. 
In this connection we cannot but point out that in no division of the 
Invertebrata are the species more valid since they are framed without 
exception not only on exceedingly well-marked external differences in 
connection with setae, etc., but also on peculiarly accentuated internal 
differences. There is no room for synonymy in any of the group. 
The restriction of the family to the Southern Hemisphere certainly 
finds its parallel in the case of many other groups, but it would seem that 
no explanation other than that of the existence at one time of a direct 
connection between the continents of the Southern Hemisphere is 
satisfactory. The Lumbriculidae which occupy a corresponding phylo- 
genetic importance are as truly restricted to the Northern Hemisphere, 
and thus we are led to conclude that each group has been evolved in the 
respective hemispheres. This being the case, we must then regard the 
existing members of the family as the descendants of an ancient 
Phreodrilid ancestor which may have flourished as early as, if not earlier 
than, Permo-Carboniferous times on ancient Gondwanaland. 
