84 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
that in this event the facts just stated might be taken 
to substantiate the theory of Mr. Herbert Spencer 
on the genesis of nerve-tissue in general. This 
theory is that which supposes incipient conductile 
tissues, or rudimentary nerve-fibres, to be differ- 
entiated from the surrounding contractile tissues, or 
homogeneous protoplasm, by a process of integra- 
tion which is due simply to use; so that just as 
water continually widens and deepens the channel 
through which it flows, so molecular-or nervous 
waves of stimulation, by always flowing through 
the same tissue-tracts, tend ever more and more to 
excavate for themselves functionally differentiated 
lines of passage. 
Such being Mr. Spencer’s theory, I applied it 
hypothetically to the above facts in the words 
which J may here quote. 
“As the successive waves beat rhythmically on 
the area of obstruction, more or less of the mole- 
cular disturbances must every time be equalized 
through these lines of discharge, which from the 
first have been almost sufficient to maintain the 
physiological continuity of the tissue. Therefore, 
according to the hypothesis, every wave that is 
blocked imposes upon these particular lines of dis- 
charge a much higher degree of functional activity 
than they were ever before required to exercise; 
and this greater activity causing in its turn greater 
permeability, a point will sooner or later arrive at 
which these lines of discharge, from having been 
almost, become quite able to draft off sufticient 
molecular motion, or stimulating influence, to carry 
