1 899] NER VOUS S\ 'STEM IN ORGANIC E VOI UTION 2 5 7 



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, i.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 

 mesemhryantlicmum, a hydroid polyp, there are stalk, root, and polyp- 

 head. If one cut oft 1 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 



