megatheriums to the north, and received mastodons
and large cats in exchange.

Some of the points, such for instance as the division of the sub-regions
into which each greater division is separated, gave rise to
considerable controversy. Wallace's final estimate of the work stands:
"No one is more aware than myself of the defects of the work, a
considerable portion of which are due to the fact that it was written a
quarter of a century too soon--at a time when both zoological and
palaeontological discovery were advancing with great rapidity, while new
and improved classifications of some of the great classes and orders
were in constant progress. But though many of the details given in these
volumes would now require alteration, there is no reason to believe that
the great features of the work and general principles established by it
will require any important modification."[4]

About this time he wrote the article on "Acclimatisation" for the
"Encyclopaedia Britannica"; and another on "Distribution-Zoology" for the
same work. As President of the Biological Section of the British
Association he prepared an address for the meeting at Glasgow; wrote a
number of articles and reviews, as well as his remarkable book on
"Miracles and Modern Spiritualism." In 1878 he published "Tropical
Nature," in which he gave a general sketch of the climate, vegetation,
and animal life of the equatorial zone of the tropics from his own
observations in both hemispheres. The chief novelty was, according to
his own opinion, in the chapter on "climate," in which he endeavoured to
show the exact causes which produce the difference between the uniform
climate of the equatorial zone, and that of June and July in England.
Although at that time _we_ receive actually more of the light and heat
of the sun than does Java or Trinidad in December, yet these places have
then a mean temperature very much higher than ours. It contained also a
chapter on humming-birds, as illustrating the luxuriance of tropical
nature; and others on the colours of animals and of plants, and on
various biological problems.[5]

"Island Life"[6] (published 1880) was begun in 1877, and occupied the
greater part of the next three years. This had been suggested by certain
necessary limitations in the writing of "The Geographical Distribution
of Animals." It is a fascinating account of the relations of islands to
continents, of their unwritten records of the distribution of plant