SECTION OF COVERED-EYED MEDUSA. 87 
intelligence, and the difficulty which intelligence 
now experiences in trying to conceive of such 
relations as disjoined. Thus it is that, even during 
the history of an individual intelligence, ‘ practice 
makes perfect,’ by frequently repeating the needful 
stimulations along the same lines of cerebral dis- 
charge, so rendering the latter ever more and more 
permeable by use. Thus it is that a child learns 
its lessons by frequently repeating them ; and thus 
it is that all our knowledge is accumulated,”* 
Rate of Transmission of Stimuli. 
The rate at which contraction-waves traverse 
spiral strips of Aurelia is variable. It is largely 
determined by the length and width of the strip; so 
* T have associated the above theory of nerve-genesis with the 
name of Mr. Spencer, because it occupies so prominent a place in 
his “‘ Principles of Psychology.” But from what I have said in 
the text, 1 think it is clear that the theory, as presented by Mr. 
Spencer, consists of two essentially distinct hypotheses—the one 
relating to the formation of nerve-tissue out of protoplasm, and 
the other to the increase of functional capacity in a nerve-fibre 
by use (a third hypothesis of Mr. Spencer relating to the 
formation of ganglion-tissue does not here concern us). The 
latter hypothesis, however, ought not to be associated with Mr. 
Spencer’s name without explaining that it has likewise occurred to 
other writers, the first of which, so far as I can ascertain, was La- 
marck, who says, “Dans toute action, le fluide des nerfs qni la 
provoque, subit un mouvement de déplacement qui y donne lieu. 
Or, lorsque cette action a été plusieurs fois répétée, il n’est pas 
douteux que le fluid qui I’a exécutée, ne se soit frayé une route, 
qui lui devient alors d’autant plus facile & parcourir, qu’il l’a 
effectivement plus souvant franchie, et qu’il n’ait lui-méme une 
aptitude plus grand a suivre cette route frayée que celles qui le 
sont moins.” (“ Phil. Zool.,”’ tom ii. pp. 318-19.) 
