252 JOURNAL OF SCIENCE. 
these only six perching birds* and 15 waders are common to 
both places. There have also been found in New Zealand one 
Australian perching bird, Aurystomus pacificus, and 7 waders, 
none of which are known in Tasmania. Of these perching birds 
Z. cerulescens first appeared in New Zealand about 30 years ago, 
H. nigricans, A. carunculatus, EF. pacificus,and G. parvirostris are 
occasional stragglers, not naturalised ; while C. plagosus migrates 
annually to and from Australia. There are also two fresh-water 
fishes, both of which go to the sea to breed, common to Tasma- 
nia and New Zealand. No fresh-water shells, and no land shells, 
with one doubtful exception,+ are known to inhabit both places ; 
no sphinx moths, and but very few insects of any kind, some of 
which may have been introduced. If we were to include allied 
species, the list of plants would be increased, but not very much. 
On the other hand some of the plants, birds, and insects may 
have migrated into both Tasmania and New Zealand from the 
north, and may never have crossed the intervening ocean ; while 
some of the birds and insects may have been helped across by 
ships, and are not therefore fair examples of natural dispersal. 
On the whole we may well be astonished that, notwithstanding 
the strong westerly cyclones and the special facilities afforded by 
petrels, no animals except a few birds and insects, and but few 
flowering plants, have been able to cross this very ancient bar- 
rier of 600 to 900 miles of ocean. This is the more remarkable 
when we remember that the floras of Kerguelen’s Land, the 
Crozets, and Marion Islands are almost identical, although the 
islands are more widely separated than New Zealand is from 
Tasmania, and they are of much smaller dimensions. The con- 
clusion is that this Antarctic group of islands must either have 
been connected, or else separated by channels much less than 
600 miles across, at some former period. 
I have already said that the greater part of the North Tem- 
perate plants spread over the southern hemisphere with the An- 
tarctic plants; and there can be no doubt but that they mi- 
grated from the north to the south along the great meridional 
chains of mountains in a “continuous current of vegetation,” as 
first shown by Sir J. Hooker, and subsequently advocated by 
Sir C. Lyell, Darwin, and Wallace. But I think that too much 
stress has been laid on the necessity for a series of alternating 
glacial epochs in each hemisphere to enable the plants to 
pass over the equatorial regions. Mr. Wallace, who is the latest 
exponent of this view, says that the “ causes (which produced 
the continuous current of vegetation from north to south) were 
the repeated changes of climate, which, during all geological 
time, appear to have occurred in both hemispheres, culminating 
* Circus gouldit, Hylochelidon nigricans, Graucalus parvirostsis, Zosterops 
cerulescens, Anthochera carunculatus, and Chalcites plagosus, 
t Paryphanta milligani,—A large species with a wide aperture, living in damp 
woods, and not at all likely to stand a voyage. New Zealand and Tasmanian speci- 
mens have not been compared, and the dentition of both is unknown. In New 
Zealand the species has been found in one locality only. 
