146 PROF. E. HCJLL ; ON THE SPREAD OF EXISTING ANIMALS 
Now there are several conceivable means by which this 
•distribution may have been effected; and they may be arranged 
under the following heads : — 
1. By human agency ; such as accidental transportation by 
ships, or direct importation. 
2. By the natural agency of winds and currents of the sea. 
3. By flotation and swimming ; and 
4. By land connection at a former period owing to the rise 
of the sea-bed, by which a laud passage was afforded 
for immigration. 
o 
1. On the first of these means there is no necessity to dwell. 
We all know that animals and plants have from time to time 
been imported into distant lands by man ; as for example the 
rabbit into Australia, and the sparrow into the United States 
•of America ; both turning out to be pests in the countries 
which have become their homes. 
2. On the subject of the natural agency of winds and 
■currents which we may term “meteorological agency,” the 
treatise of Dr. Wallace, one of the founders of zoogeography, 
takes the first place amongst recent writers,* followed by the 
work of Dr. Scharff, which has given rise to the present essay, 
in which I shall have occasion to draw attention to the 
•divergence of views of these writers. 
3. The third means of distribution need not detain us, as it 
is of rare occurrence for distant islands ; but the fourth is that 
which will require our attention as one of great importance. 
4. Range of the Subject. — The able paper read before the 
Institute last session by Prof. Logan Lobleyt may be considered 
.as introductory to the present subject, in that it dealt with the 
•origin of the European fauna. On this occasion we have to 
consider the problem, how to account for the existence of some 
of these forms in the far distant islands of the Atlantic ; and to 
investigate the very divergent views of Wallace and Scharff on 
this problem. And we shall also endeavour to ascertain how the 
fact of the great uprise of the lands and bed of the adjoining 
•ocean which has been demonstrated by the formation of the 
submerged continental platform and the drowned river-valleys, 
throws light on the presence of these island forms of life.}. 
* Island Life, by Dr. A. I’. Wallace, 2nd Edit., 1892. 
t Trans. Viet. Inst., vol. xxxix, p. 102. 
} “On the subject of the plant distribution amongst the islands of the 
ocean.” Dr. Guppy’s able paper has already been laid before the Institute. 
See Trans., vol. xxxix, p. 167. 
