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-tract^, 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 I 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 

 throuQfh these lines of discharo-e, 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 

 v/hich these lines of discharge, from having been 

 almost, become quite able to draft off sufficient 

 molecular motion, or stimulating influence, to carry 



