636 TRANSACTIONS OF SECTION I. 
temperature. It is evident that a great advantage in the struggle for existence 
was gained by the first animals which succeeded in securing thermal as well as 
chemical constancy of environment for their cells, thus rendering them indepen- 
dent of changes in the external medium. It is interesting to note that the 
maintenance of the temperature of warm-blooded animals at a constant height 
is a function of the higher parts of the central nervous system. An animal 
with spinal cord alone reacts to changes of external temperature exactly like a 
cold-blooded animal, the activity of its chemical changes rising and falling with 
the temperature. In the intact mammal, by accurately balancing heat loss 
from the surface against heat production in the muscles, the central nervous 
system ensures that the body fluid which is supplied to all the active cells has a 
temperature which is independent of that of thesurrounding medium, These are 
fundamental examples of adaptation effected by creation of an environment 
peculiar to the animal. Numberless others could be cited which differ only in 
degree from the activity of man himself. In some parts of this country, for 
instance, the activity of the beaver in creating an artificial environment has 
until lately been more marked than that of man himself. We are not justified, 
then, in regarding mankind as immune to the operation of natural forces which 
have determined the sequence of life on the surface of the globe. The same 
laws which have determined his evolution and his present position as the dominant 
type on the earth’s surface will determine also his future destiny. 
We are not, however, dealing with or interested in simple survival. Lower 
forms of life are probably as abundant on the surface of the globe as they were 
at any time in its history. Survival, as Darwin pointed out, is a question of 
differentiation. When in savage warfare a whole tribe is taken captive by the 
victorious enemy, the leaders and fighting men will be destroyed, while the 
slaves will continue to exist as the property of the victors. Survival, then, may 
be determined either by rise or by degradation of type. Success involves the 
idea of dominance, which can be secured only by that type which is the better 
endowed with the mechanisms of adaptation required in the struggle against 
other organisms. : 
Among the many forms of living matter which may have come into being 
in the earlier stages of the history of the earth, one form apparently became 
predominant and must be regarded as the ancestor of all forms of life, whether 
animal or vegetable, viz., the nucleated cell. The almost complete identity of 
the phenomena involved in cell division throughout the living kingdom indicates 
that all unicellular organisms and allorganisms composed of cells have descended 
from a common aneestor, and that the mode of its reproduction has been im- 
pressed upon all its descendants throughout the millions of years which have 
elapsed since the type was first evolved. The universal distribution of living cells 
renders it practically impossible for us to test the possibility of a spontaneous 
abiogenesis or new formation of living from non-living matter at the present 
time, We cannot imagine that all the various phenomena which we associate 
with life were attributes of the primitive life stuff. Even if we had such stuff 
at our disposal, it would be difficult to decide whether we should ascribe the 
possession of life to it, and there is no doubt that any such half-way material 
would, directly it was formed, be utilised as pabulum by the higher types of 
organism already abounding on the surface of the globe. 
Integration and Differentiation. 
An important step in the evolution of higher forms was taken when, by the 
aggregation of unicellular organisms, the lowest metazoon was formed. Initsmost 
primitive forms the metazoon consists simply of a cell colony, but one in which all 
individuals are not of equal significance. Those to the outer side of the mass, 
being exposed to different environmental advantages from those within, must 
even during the lifetime of the individual have acquired different characteristics. 
Moreover, the sole aim of such aggregation being to admit of co-operation by 
differentiation of function between the various cell units, the latter become 
modified according to their position, some cells becoming chiefly alimentary, 
others motor, and others reproductive. Co-operation and differentiation are, 
however, of no use without co-ordination. Each part of the organism must be 
