340 PROCEEDINGS OF SECTION D. 
entry; and we may, then, regard the point of entry into 
Australia as in the north-east. 
The sparseness of the Acanthodrilids in this great conti- 
nent of Australia may indicate a very brief connection with 
their home, but more probably it is a result of their replace- 
ment by more highly-developed northern genera; while 
their absence in the south seems to indicate the absence of a 
connection with Antarctica during the existence of these 
worms on that land. This is further emphasised by the 
total absence of Cryptodrilids from South America and 
South Africa. 
1 am not denying the probability of a continuity of land- 
connection between Tasmania and Antarctica at some 
period—this appears to be required to explain various dis- 
tributional facts—but the earthworms indicate that this 
connection was an early one—earlier, even, than that of 
New Zealand and the Southern continent. 
As I have remarked above, the Cryptodrilids, z.e., Plutel- 
dus, Notoscolex, and Megascolides, appear to be descendants 
of the Acanthodrilids; and, from the evidence available, we 
are led to look upon the Oriental region as the probable 
centre of distribution of this group. 
This evolution must have taken place at a time when the 
present islands of Malay Archipelago and Melanesia were 
in more direct continuity—not necessarily a continuous land- 
surface, but forming an area sufficiently large to permit the 
development of Cryptodrilids, and from them the genus 
Megascoler. These genera must have spread westward 
over the southern portion of the Oriental region, and at an 
earlier period migrated southward into Australia. 
It would take too long to discuss fully the approximate 
period of the westward migration, and the various land- 
changes that necessarily took place; but we have evidence 
from the peculiar distribution of Placental mammals in 
these islands that they have undergone various upheavals 
and depressions, thereby producing a variety of inter- 
communications. It appears probable that the entry of 
Cryptodrilids and Megascolex into Australia coincided with 
the entry of marsupials, in late Mesozoic or the early Ter- 
tiary. Here they over-ran the continent, each genus giving 
rise to one or several allied genera, and thus ousting the 
original Acanthodrilids, which perhaps never reached very 
far to the south. 
It is difficult to account for the absence of Cryptodrilids 
in the mainland of the Oriental region, but it may be that 
further search for them will be repaid. Nevertheless, there 
