Characters, Hereditary and Acquired. 83 



the machinery is not sufficiently perfected for the 

 adequate discharge of that function. In this impor- 

 tant respect it differs from the otherwise closely 

 analogous reflex action of the frog, whereby the 

 foot of the hind leg is enabled to localize with 

 precision a seat of irritation on the side of the 

 body. But this beautiful mechanism in the frog can- 

 not have sprung into existence ready formed at any 

 historical moment in the past history of the phyla. 

 It must have been the subject of a more or less 

 prolonged evolution, in some stage of which it must 

 presumably have resembled the now nascent scratch- 

 ing reflex of the dog, in making merely abortive 

 attempts at localizing the seat of irritation — supposing, 

 of course, that some physiologist had been there to 

 try the experiment by first removing the brain. 

 Now, even if one could imagine it to be, either in the 

 frog or in the dog, a matter of selective importance that 

 so exceedingly refined a mechanism should have been 

 developed for the sole purpose of inhibiting the bites 

 of parasites — which in every normal animal would 

 certainly be discharged by an intentional performance 

 of the movements in question, — even if, in order to 

 save an hypothesis at all costs, we make so violent 

 a supposition as this, still we should do so in vain. 

 For it would still remain undeniably certain that 

 the reflex mechanism is not of any selective value. 

 Even now the mechanism in the dog is not sufficiently 

 precise to subserve the only function which occasionally 

 and abortively it attempts to perform. Thus it has 

 all the appearance of being but an imitating shadow 

 of certain neuro-muscular adjustments, which have 

 been habitually performed in the canine phyla by a 



G a 



