404 TUB INFLUENCE OF LIVING SURKOUNDINGS. 



easy to deduce from analogous caiises the somewhat more perfect 

 likeness in form and colour between Cladocora and the un- 

 described Myxicola. 



Still, true mimicry might, no doubt, be developed from such 

 a case of extreme resemblance between two quite distinct, crea- 

 tures. Supposing that some animal not hitherto living in the 

 sea at Port Mahon were to be introduced there which was able to 

 capture the Annelida wherever their unlikeness to the objects 

 around them— as the sand, sponge, <fec. — rendered them con- 

 spicuous, they would only find the protection they would need 

 by living associated with the coral, because there only could 

 they be effectually concealed. And if the enemy — pursuing 

 them even among the polyps Of the Cladocora — should have 

 learned to regard the polyps as dangerous foes whose fine sting- 

 ing threads were capable of inflicting much injury, a perfectly 

 characterised case of true mimicry might be developed from this 

 instance, originating in simple shelter. 



The theoretical possibility of the process thus indicated can- 

 not, I think, be denied ; but then the question arises whether 

 many cases of mode of colouring and resemblance which we 

 have hitherto been disposed to regard as cases of exquisite 

 mimicry may not have originated in the same way as the 

 spurious mimicry of the Myxicola. And here we find ourselves 

 brought face to face with the same conclusion that we have 

 become familiar with in each separate chapter of this work, and 

 which I must once more repeat : Namely, that no power which 

 is able to act only as a selective, and not as a transforming 

 influence can ever be exclusively put forward as the proper e&- 

 cient cause — causa ejfficiens — -of any phenomenon. In all cases, 

 including those of ihimicry, the point finally must be to in- 

 vestigate the causes which may have availed to produce, by 

 their direct action, any advantageous and protective change of 

 colouring; it was not until the change had actually taken place 

 that selection between the better or worse endowed individuals 

 could lead to the further development of the adva,ntageous cha- 

 racter. It is extremely difficult to decide in particular cases — ^in 

 most, indeed, it is impossible — the precise point where one ceases 

 and the other begins to act. But it is precisely by reason of the 



