14 
VOHKSHIRE naturalists' UNION. 
Some scientists are inclined tu regard tlie highly specialized 
species in which elaboration of structure or function has been carried 
to the marvellous extent so characteristic of certain tropical and 
archaic species, as evidences of potential dominance or superiority 
over the secondarily simplified forms of t\w European region, in 
which the efficiency and adaptability of their physiological processes 
give them a sui)eriority which is displayed by the way in which 
these large and extremely specialized forms of life are being driven off 
by the more highly endowed European species. 
Others, disregarding tlieir ])rimitive nature, desciibe the archaic 
and dying forms characteristic of xVntarctica and othei- primitive 
southern regions, as advancing northwards and occupying districts 
already tenanted by stronger and more highly developed races, or even 
suggest Antarctica as a great evolutionary centre and source of 
dispersion apparently on account of many of the most primitive 
forms of life having found temporary sanctuary in or neai- the most 
extreme parts of the southern hemisphere and in the erroneous belief 
that the i)resent day abode or metropolis of ancient forms of life 
indicates their real place of origin. 
It is, however, highly improbable that these, the very feeblest of 
living species, representing groups originally inhabiting the northern 
hemisphere, but long ago expelled or in process of expulsion from the 
more northern countries by their more highly endowed successors, 
can extend their range to the detriment of species which are ever 
driving them southward to their future inevitable extinction. 
That the organic life of such primitive countries is weak and 
impotent and quite incapable of any aggressive advance or occupation 
of other lands is shown clearly by its startingly rapid destruction 
or retreat when brought into direct conflict or competition with the 
stronger forms of Europe, and in a lesser degree with those of Asia, 
whether these be moUusks, earthworms, birds, insects, plants, mammals 
or man himself. 
In such cases the native species rapidly disappear and the new 
comers take possession of the land, driving off or destroying the 
original occupants so that in many of these weaker countries the 
native moUusks, worms, birds, ])lants, animals and men have (|uite 
disappeared from the neighbourhood of the settlements and only the 
dominant F^uropean s))ecies can now be found. 
For a notable instance of the marked exercise of this colonizing 
power, I am indebted to Mr. J. H. Ponsonby who informs me that a 
form of the Heath Snail {HelLv itala), a xerophilous species which 
in Europe is oidy conditionally dominant, being more or less restricted 
to dry and arid lands, was some years ago unwittingly transferred, 
probably in grass seed, to the vicinity of Levens, South Australia, 
where it has now overspread hundreds of square miles on the York 
Peninsula, and is so exceedingly abundant that the herbage is in 
])laces white over with the countless millions of their shells. 
