THE PRINCIPLES OF BIOLOGY. 
167 
spring. It is obvious that there are several other early 
species which may be expected to occur about here, and these 
will no doubt turn up in future years. I shall be glad to 
receive specimens of these from any members of the Birming¬ 
ham Societies who may be fortunate enough to meet with 
them and kind enough to help me in completing this branch 
of the Fungus Flora of the district. 
THE PRINCIPLES OF BIOLOGY* 
BY HERBERT SPENCER. 
Exposition of Chapters XI. and XII., “Direct Equilibration ” 
and “ Indirect Equilibration.”! 
BY CONSTANCE C. W. NADEN. 
By Mr. Spencer’s expression “ a moving equilibrium,” we 
are to understand a mechanism the parts of which are in a 
state of constant activity, and yet preserve equilibrium with 
regard to each other and to external forces. The mechanism 
may be organic or inorganic, its component parts may be 
atoms, heavenly bodies, or the organs of the human frame, 
but their movements, of whatever kind, must always be 
rhythmic. The Solar System is a moving equilibrium—so is 
a watch—so too is a plant or animal. 
Now if any fresh incident force affects the mechanism it 
will either destroy the rhythmic motions altogether, as when 
I wind my watch too far and break its mainspring ; or it will 
go on modifying the motions till a new equilibrium is 
established, as when I move the regulator of my watch from 
slow to fast. 
Every plant and animal is daily receiving from without 
fresh energy, in the place of that which it daily expends. Its 
food supplies it with heat, which is converted into various 
modes of motion. But the resulting equilibrium may be dis¬ 
turbed by a lack of food, by altered climate, by the intro¬ 
duction of hostile or helpful organisms, by increased or 
diminished power of assimilation, or by other natural causes. 
A change of state will gradually be brought about; the 
primary disturbance originating secondary and tertiary dis- 
* Transactions of the Birmingham Natural History and Micro¬ 
scopical Society — Sociological Section. 
t Miss Naden’s paper on Part III. of Mr. Herbert Spencer’s 
Principles of Biology , Chap. I., “Preliminary;’' Chap. II., “The 
Special Creation Hypothesis;” and Chap. III., “The Evolution 
Hypothesis,” has been published in a separate form. 
