32 
PROOFS OF EVOLUTION. 
nervous system, the nutritive system, and the 
blood system ; and from these follow the multitud¬ 
inous branchings to the highest stage of differen¬ 
tiation in the ontogenic series. Tracing any one 
of these groups, as the nervous system, we find 
it differentiates once more, forming the cerebro¬ 
spinal and ganglionic systems, each having differ¬ 
ent functions. The cerebro-spinal again differen¬ 
tiates into two systems, the voluntary and reflex,— 
these still again branching out into sensory and 
motor centres and fibres. The sensory-fibres 
branch out into the five senses with their separate 
functions. Take any one of the senses, as touch, 
and we observe that the nerve-fibres are not all 
alike. Some are sensitive to heat and cold; others 
to pressure. The nutritive and blood systems 
have, likewise, their special lines of differentiation, 
culminating in all the different organs, parts and 
functions of the animal body. And this is the 
process of every life and every birth. 
One of the most startling as well as one of the 
strongest proofs of evolution, is found in the fact 
that in Embryonic growth, each individual passes 
through all the successive stages which have 
preceded in the line of its tribal history. In other 
words, philogeny is repeated in ontogeny; the race 
