1899] WERVOUS SYSTEM IN ORGANIC EVOLUTION 257 
begin to make their appearance. Excitability, while still pervading 
the whole organism, becomes localised with greater intensity in some 
parts than in others; along some lines than along others (sense organs, 
nerves, and nerve-centres); in other parts contractibility becomes the 
salient character (muscles). To illustrate this progressive elaboration 
of a nervous system, we may select—(1) an amoeba; (2) a jelly-fish ; 
(3) a frog; (4) a man.” Thus we learn how gradually the nervous 
system is evolved, becoming, as organisation increases, more and more 
specialised in diversity of function, from, let us assume, invisible 
threads of granular protoplasm to the gray matter of the human brain, 
and the associated prolongations throughout the body. We must also 
recognise that the nervous energy is gradually diversified and intensi- 
fied as evolution proceeds upward, from a mere automatic action in 
the protozoon, to the varied and diversified functions of man, mental 
as. well as physical. 
In his “ Principles of Biology,’ Mr. Herbert Spencer says: “In 
whatever way it is formulated, or by whatever language it is obscured, 
this ascription of organic evolution to some natural aptitude possessed 
by organisms, or miraculously imposed on them, is unphilosophical. 
It is an assumption no more tenable than the assumption of special 
creation, of which, indeed, it is a modification, differing only by the 
fusion of separate unknown processes into a continuous process.” It 
seems to me that, in making the above statement, Mr. Spencer wholly 
overlooks the power of the nervous system in rendering organisms 
capable of reacting to the influences of the environment. We may 
confidently ask, if the organism does not possess such a function, to 
what must we attribute the power of reaction? for unless we do 
recognise such a power inherent in the organism, rendering it capable 
of being gradually modified in relation to its needs, wants, or desires, 
and the incident forces of the environment, the only alternative 
is to believe in a power otherwise derived, 7.e. in special creation or 
creations. 
In addition to the evidence already adduced, I may take as an 
illustration of the power of the organism to respond to its needs in a 
definite way, Loeb’s experiments to produce heteromorphosis, as cited 
in “The Biological Problem of To-day,” by Hertwig. “In Tubularia 
mesembryanthemum, a hydroid polyp, there are stalk, root, and polyp- 
head. If one cut off the head, a new head will be formed in a few 
days, this being a case of regeneration. On the other hand, a hetero- 
morphosis may be produced by modifying the experiment as follows :— 
Both root and head must be cut off from the stem; if the lopped 
piece of the stem be stuck in the sand of the aquarium by the end 
that bore the head, then the original aboral pole, in a few days, pro- 
duces a head; if the lopped piece of stem be supported horizontally 
in the water, then each end produces a head.” Hertwig goes on to 
give illustrations to show how, in other organisms, heads, tentacles, and 
