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PRINCIPLES OF BIOLOGY. 
THE PRINCIPLES OF BIOLOGY. 
BY HERBERT SPENCER. 
Exposition of Part III. Chapter IV. 
BY DR. WILLIAM L. HIE PE. 
Iii the two first chapters of the third part, Mr. Herbert 
Spencer gives the general aspect of the theory of evolution, 
and contrasts it with the older belief in special creation. The 
next four chapters, which form the subject of our present 
discussion, are devoted to the investigation, how far certain 
zoological phenomena are in harmony with the evolution 
theory. These phenomena are those of classification, embry¬ 
ology, morphology, and distribution. So far from finding 
that these phenomena are not in harmony with the theory of 
evolution, we shall find that they cannot be satisfactorily 
explained by any other; that they follow as a necessary 
consequence from this theory, and they form, therefore, the 
basis of the most convincing and powerful arguments in 
favour of it. We shall now consider these arguments a little 
more in detail. 
When we study the system of classification of the organic 
world, we find that the whole is divided into two main groups 
or kingdoms ; animals and plants. Each of these main groups 
is divided into a number of secondary groups or sub¬ 
kingdoms. Each sub-kingdom into classes, and so on till 
we come to species aud varieties. Calling, with Mr. Spencer, 
a division of high degree a group, and one of a relatively 
lower degree a sub-group, we find, further, that the differences 
which distinguish groups are great in degree and radical in 
kind, i.e ., they concern, as a rule, physiologically important 
organs. Differences of sub-groups are small in degree and 
do not concern important organs ; in fact, they are often so 
small that it is impossible, or nearly so, to detect them. As 
an example, Mr. Spencer mentions the groups and sub-groups 
of the human species. The different nations which form the 
group of the Scandinavian races do not differ so much from 
each other as the whole of the Scandinavian races differ from 
the whole of the Celtic races. Again we find a greater 
difference between the northern races and the southern races, 
and finally we find the greatest difference between the largest 
groups, i.e., the Aryan stock, the Mongolian stock, and the 
Negro stock. 
We find the same with the different languages, from the 
most nearly related dialects to the widely different eastern 
and western languages. In languages we know that the 
