160 
REVIEWS. 
ANIMAL LIFE* 
F EW naturalists can claim to speak with more authority than Prof. 
Semper. A long residence in those rich tropical Eastern countries, the 
natural productions of which we know chiefly from the descriptions of 
hurried travellers, or from the researches of scientific expeditions, familiarized 
him with the structure and hahits of a most varied assemblage of animal 
forms ; and his previous training enabled him to make good use of the un- 
rivalled opportunities of study thus afforded him. Accordingly it is no 
great wonder that his volume of the ‘ International Science Series,’ lately 
published, should he unquestionably one of the most interesting contribu- 
tions to zoological literature that has appeared for years. 
Holding the doctrine of the evolution of organic forms as proved, Prof. 
Semper considers that there has been sufficient theorizing on- the subject, 
and that what we now require is an exact investigation, by observation and 
experiment, of the processes by which changes are produced in the organism. 
Thus he says in his Preface : — ‘ The popular cant about “ Biogenetic princi- 
ples and the falsification of Ontogenesis — the laws of inheritance at corre- 
sponding periods of fife, or the correlation of organs — Ontogeny and Phylogeny 
— variability and heredity ” — is put out of court as useless ; for these are 
merely axiomatic expressions for a sum of identical or correlative pheno- 
mena, of which the essential nature is in no way revealed by them ; ’ and it 
is with the view of indicating the road which he thinks should be taken to 
furnish the true explanation of these generalized expressions that his present 
book was written. 
Variability, he thinks, of all the properties of the organism ‘is that 
which may first and most easily be traced by exact observation to its efficient 
causes;’ and it is to the phenomena and causes of variation in animals 
that his book is chiefly devoted. But it has a further limitation. Prof. 
Semper is of opinion that the action of conditions external to the organism is 
a much more potent factor in the modification of the latter than is supposed 
by many naturalists of the so-called Darwinian school, or, in fact, by Mr. 
Darwin himself, at least in his earlier writings on the origin of species. 
* The Natural Conditions of Existence as they affect Animal Life. By 
Karl Semper. 8vo. London : Kegan Paul & Co. 1881. 
