33 
NOTICES OF NEW BOOKS. 
Island Life; or, the Phenomena and Causes of Insular Faunas 
and Floras, including a revision and attempted solution of 
the problem of Geological Climates. By Atrrep Russe 
Wattacr, Author of ‘The Malay Archipelago,’ &c. Demy 
8yo, pp. 512, with twenty-six Maps and Illustrations. 
London: Macmillan & Co. 1880. 
TuEeRE must be few, if any, of our readers who have not 
derived both pleasure and profit from a study of Mr. Wallace's 
‘Geographical Distribution of Animals,’ published in 1876. The 
present volume, which may be considered as a popular supplement — 
to, and completion of, that work, will afford no less eratification 
and instruction. It deals with highly important and interesting 
problems, and embodies a mass of facts collected and arranged 
with admirable skill and precision. Although at first sight some- 
what fragmentary and disconnected, it is really the development 
of a clear and definite theory, and its application to the solution 
of a number of biological problems. That theory is, briefly, that 
the distribution of the various species and groups of living 
things over the earth’s surface, and their aggregation in definite 
assemblages in certain areas, is the direct result and outcome of 
a complex set of causes which may be grouped as “ biological” 
and “ physical.” 
The biological causes, to use the author’s own words, are 
mainly of two kinds—virst, the constant tendency of all 
organisms to increase in numbers and to occupy a wider area, 
and their various powers of dispersion and migration through 
which, when unchecked, they are enabled to spread widely over 
the globe; and, secondly, those laws of evolution and extinction 
which determine the manner in which groups of organisms arise 
and grow, reach their maximum, and then dwindle away, often 
breaking up into separate portions which long survive in very 
remote regions. 
The physical causes are also mainly of two kinds. We have, 
first, the geographical changes which at one time isolate a 
whole fauna and flora, at another lead to their dispersal and 
intermixture with adjacent faunas and floras; and, secondly, 
F 
