20 
YORKSHIRE NATURALISTS' UNION. 
Tlie Megascolecid^, judged by their geographical distribution, 
stand next the Lumbricids in order of evolution and doniinancy, and 
occupy Eastern Asia, their range extending fn^ni Japan and China 
to the Malay Archipelago and Australasia ; areas in general corre- 
spondence with those of the Euadeniate and Epiphallogonous Helices, 
which possess exactly analogous dominating power. 
The species of this group, and especially its rearmost and latest 
evolved genus Pheretima, have great powers of dispersal and coloniza- 
tion everywhere, except in the regions dominated by the Lumbricidir. 
The remarkable correlation of the distribution of the Megascolecids 
with the Euadeniate and Epiphallogonous Helices in the Old World 
is also shown in America, where representative species occupy precisely 
similar geographical positions along the shores of the Pacific Ocean, 
and have identically the same dominating power, being the highest 
earthworms in that region. 
The (tE0SC0LECid.i<: are, tn^m their geographical position, evidently 
of more ancient origin than the two preceding groups, and that they 
constitute a more archaic type is shown by the general absence of 
dorsal pores : such absence being an attribute of atpiatic life, and a 
characteristic of their aquatic ancestors. 
This group is quite analogous to the molluscan group Epiphallogona, 
having the same degree of dominancy over species and groups of more 
ancient origin, and being regressive before the more recently evolved 
and modern Megascolecidw and Lmnhricidw, exactly like their 
molluscan analogues, and inhabiting corresponding regions, being 
found in South Africa and Madagascar. 
In the New World this group has followed the same path as 
described for the mollusca, and is now found in South America and 
the West Indian Islands, in positions exactly corresponding to those 
of the analogous or representative molluscan groups. 
The AcANTHODRiLiDiE, whicli are analogous to the most primitive 
group of Helices, the Protoyona, and are the simplest and most 
archaic of their kind, as is shown by the absence of dorsal pores and 
their partially aquatic habits ; tliey also originally arose in the 
European region, and in their time were the dominant race of 
earthworms, but have been gradually driven from country to country, 
until at the present day they are restricted, with other feeble forms 
of life, to the most remote regions of the world, or those most 
difficult of access by natural means from Western Pala'arctica. 
In addition to the southern extremities of continental lands where 
the Acanthodrilids are still dominant, they are the prevailing native 
type of worms in the Eastern United States, being represented by 
Microscolex, Diplocardiinw and Ocnerodrilinw all of which groups are 
closely allied to Notiodi'ilii^ the most primitive earthworm known, and 
standing nearest the assumed generalized form from which the earth- 
worms arose ; this again confirming the unity of plan governing 
life distribution. 
