REVIEWS. 
161 
From this point of view the question of the variability of organisms is treated 
in a most thoughtful manner by Prof. Semper, and illustrated by the citation 
of a multitude of examples from all divisions of the animal kingdom, and in 
many cases founded on the personal observations of the author. 
In the action of external conditions of existence upon animals, Prof. 
Semper distinguishes transforming and selective influences ; hut, in his 
arrangement of his subject, he divides the external agents into those 
belonging to inorganic or inanimate nature, including under this term the 
food which, although it may be derived from living organisms, does not 
become food until after they are dead ; and those due to living organisms, 
and especially to living animals of other species. Both these series include 
both transforming and selective influences. 
Under the former category we have, besides food already mentioned, the 
influence of light and temperature, that of the condition of the water upon 
aquatic animals, and of the air upon others, the influence of currents upon the 
distribution of animals, and some other points ; under the second, the action 
of parasites and hybridization indirectly transforming animals, and the 
consequences of the competition among animals in its selective in- 
fluence on the organisms. In connexion with the influence of water 
in motion, Prof. Semper furnishes his readers with an exposition of 
his views on the formation of coral reefs, illustrated especially by his 
own investigations on the Pelew Islands, which, as is well known, 
have led him, in opposition to the generally received views of Mr. 
Darwin, to the opinion that here, at any rate, the evidence is in favour of 
the occurrence of upheaval of the region during the formation of the reef. 
So far as the Pelew Islands are concerned, there is no doubt the author 
makes out a very strong case ; but whether it is an exceptional one remains 
to be seen. Under any circumstances, his description of the Pelew reefs 
will be read with much interest. 
Throughout his little book, indeed, the amount of interesting information 
on the structure and habits of animals that Prof. Semper lays before his 
readers is very great ; and the statements in the text are supplemented by a 
series of most valuable notes on points of detail, forming an appendix. The 
book is very freely illustrated with well-executed woodcuts, and is certainly 
one of the most attractive volumes on natural history that has appeared for 
several years. 
A POLAR RECONNAISSANCE.* 
T HIS most interesting book is intended by Captain Markham not only as 
an account of a voyage made by him in company with Sir H. Gore 
Booth to the seas surrounding Novaya Zemlya, but also as an argument in 
* A Polar Reconnaissance , being the Voyage of the 1 Ishjorn ’ to Novaya 
Zemlya in 1879. By Albert H. Markham. 8vo. London : C. Kegan Paul 
& Co., 1881. 
NEW SERIES, VOL. V. NO. XVIII. M 
