THE PRINCIPLES OF BIOLOGY. 
179 
Clay, although impermeable, will often contain 10 per cent, 
of water by weight, and when apparently quite dry, often 
more than half that amount. I have made these remarks 
because it seems to be rather a common belief that water 
only travels in the Middle Lias by means of open fissures, 
whereas the great mass of the rock is engaged in supplying 
these fissures with water. 
(To be continued.) 
THE PRINCIPLES OF BIOLOGY. 
BY HERBERT SPENCER. 
Part Y.—“ Physiological Development.” 
Exposition of Chapters I. to Y. 
BY KINETON PARKES. 
In discussing the problems of physiology generally Mr. 
Spencer reminds us that we must use the word “physiology ” 
in a sense co-extensive with the sense in which the word 
•‘morphology” was used in the previous part. 
The various processes of animal and plant life must be 
considered in a way analogous to that in which their structures 
were considered. So that in this consideration the words have 
a far greater significance than is generally attributed to them. 
They are used to include respectively “ All the general phe¬ 
nomena .... which illustrate the processes of integration 
and differentiation characterising evolution in general,” and 
“ the evidences of those differentiations and integrations of 
organic functions which have simultaneously arisen.” 
The enquiry pursued in these chapters is “How hetero¬ 
geneities of action have progressed along with heterogeneities 
of structure ,” in them are traced out the various differentiations 
which have taken place in the life processes, and how these 
differentiations have been the accompaniment of the changes 
which have taken place in the bodies of the various organisms 
that are known to us. At the end of this enquiry we shall 
realise how fully life itself consists of “ a definite combina¬ 
tion of heterogeneous changes, both simultaneous and 
successive.” 
One of the first facts that is noticed, in a practical ac¬ 
quaintance with vegetable forms, is the difference between 
their external and internal parts. However lowly the organism 
