378 NATURAL SCIENCE [December 
as involving the continuous adjustment of internal relations to 
external relations, is developed. To this part a new chapter on the 
Dynamic Element in Life is added. 
After an indication of the scope of biology, the inductions of 
the science are considered in Part II. Generalizations as to 
growth, development, adaptation, genesis, heredity, and variation, 
ave formulated and illustrated ; the classification and distribution of 
organisms are considered, and the foundations are thus laid for the 
erection of an aetiological superstructure. The special-creation 
hypothesis is contrasted with that of evolution; the arguments for 
the latter are marshalled; and the causes of evolution discussed. 
Internal and external factors are distinguished ; and the phenomena 
are explained as due to the joint action of (1) direct equilibration 
through the inheritance of acquired modifications, and (2) indirect 
equilibration through the survival of the fittest in the process 
termed by Darwin ‘natural selection. A concluding chapter 
on Recent Criticisms and Hypotheses, in which any inherent 
tendency to evolution along predetermined lines is rejected, brings 
the volume to a conclusion, save for Appendices, amongst which 
are the Contemporary Review articles on the Inadequacy of 
Natural Selection. 
In the additional matter of the present edition Mr Herbert 
Spencer would probably lay most stress on the chapter which deals 
with the Dynamic Element in Life, and on the arguments in favour 
of direct equilibration through the inheritance of acquired modifica- 
tions. While other additions, such as those on protoplasm, on 
metabolism, on nuclear changes, on embryological development, and 
on classification, serve mainly (for there are original suggestions) to 
bring the work into line with modern biological conclusions, the 
supplementary discussion of the Dynamic Element in Life is in 
touch with the author’s distinctive philosophical tenets, and the 
arguments for direct equilibration are adduced in support of 
biological conclusions which Myr Spencer regards as of extreme 
importance. It seems desirable therefore to direct attention 
specially to these -points. 
After leading up to a conception of Life as the definite com- 
bination of heterogeneous changes, both simultaneous and successive, 
in correspondence with external co-existences and sequences, and 
after urging that the degree of life varies as the degree of corre- 
spondence, Mr Spencer briefly indicates certain vital processes which 
remain outside the conception as thus formulated, and contends 
that all cases “exhibit that principle of activity which constitutes 
the essential element in the conception of life.” This he terms the 
dynamic element in life; and he asks whether it is inherent in 
organic matter or is something superadded. The notion of a super- 
