Mr. T. V. WoUaston on the Tarphii. 381 



have treated them equally as a truth of reason. But this was uu- 

 necessaiy, for I am not now discussing the question as to where the 

 several Knes of demarcation are to be drawn, but am simply assert- 

 ing the broad fact that they have an abstract existence somewhere, 

 rigidly and positively defined. For, in arguing the reality of limits, 

 it must not be supposed that it is with any hope of making it easier 

 to define practically where the boundary lines are to be placed. That 

 is altogether another matter, and one which must be solved approxi- 

 mately by a careful and laborious investigation, for it cannot be 

 arrived at by dialectics ; and we must be content therefore, gene- 

 rally, to leave it in the hands of those naturahsts who have devoted 

 their lives to the investigation of the particular groups. With our 

 short-sighted faculties, indeed, the limitation of sjiecies always will 

 and must be, in a great measure, subject to dispute; for our powers 

 of judgment diff^er, and are not stereotyped : but to use that fact as 

 an argument against the existence of limits altogether is in the 

 highest degree unphilosophical, and can only resTilt from a misappre- 

 hension of the class of truth to which they necessarily belong. 



If, then, I had to sum up in a few words what has been said, it 

 would be to the effect, that these Atlantic and Sicilian Tarphii, 

 with their "nearly allied" Inchan representatives, were, and must 

 have been, as nuclei, aboriginally distinct. Whether we view them 

 structurally or geographically, this conclusion is alike forced upon 

 us by evidence which it seems impossible to resist, — whilst there are 

 the strongest reasons for suspecting that the modem theory which 

 would pretend to derive them all fi'om a common ancestor, so far 

 from being a philosophical one, is based upon a fallacy and an 

 ignoring of the distinction between two opposite classes of truth. 

 To render this latter fact the more ob%'ious, I have endeavoured to 

 show that the doctrine of limits is not a mere concoction of the 

 brain, but that it embodies a reality which no amount of sophistry 

 or ingenious special pleading can set aside, and that it is not the 

 less to be believed because, Hke half the tniths of which the human 

 mind is cognizant, it is a " truth of reason," and therefore not 

 proveable, in its entirety, to our imperfect understanding, like a 

 truth of sense. As for the question (and it is an exceedingly inter- 

 esting one) of limited modification from external influences of every 

 kind, we may safely leave it to be decided on its own merits ; but 

 let us be veiy cautious how we employ the results arrived at in this 

 restricted field of research to siibvert fundamental principles, which, 

 if they are to be assailed at all, must be approached in a different 

 manner and from a totally different direction, and which would 



