INADEQUACY OF NATURAL SELECTION, ETC. 613 



animals have simply degenerated through disuse." After giving 

 instances of rapid degeneration of disused organs, he argues that 

 if " the effects of disuse are so striking in a single life, we should 

 certainly expect, if such effects can be transmitted, that all traces 

 of an eye would soon disappear from a species which lives in the 

 dark." Doubtless this is a reasonable conclusion. To explain 

 the facts on the hypothesis that acquired characters are inheri- 

 table, seems very difficult. One possible explanation may, in- 

 deed, be named. It appears to be a general law of organization 

 that structures are stable in proportion to their antiquity — that 

 while organs of relatively modern origin have but a comparatively 

 superficial root in the constitution, and readily disappear if the 

 conditions do not favour their maintenance, organs of ancient 

 origin have deep-seated roots in the constitution, and do not 

 readily disappear. Having been early elements in the type, and 

 having continued to be reproduced as parts of it during a period 

 extending throughout many geological epochs, they are compara- 

 tively persistent. Now the eye answers to this description as 

 being a very early organ. But waiving possible explanations, 

 let us take the particular instance cited by Prof. Weismann and 

 see what is to be made of it. He writes : — 



" The caverns in Carniola and Cai-intliia, in which the blind Proteus and 

 so many other blind animals live, belonj^ geologically to the Jurassic 

 formation ; and although we do not exactly know when for example the 

 Proteus first entered them, the low organization of this amphibian certainly 

 indicates that it has been sheltered there for a very long period of time, and 

 that thousands of generations of this species have succeeded one another in 

 the caves. 



" Hence there is no reason to wonder at the extent to which the degene- 

 ration of the eye has been already carried in the Proteus ; even if we assume 

 that it is merely due to the cessation of the conserving influence of natural 

 selection." * 



Let me first note a strange oversight on the part of Prof. 

 Weismann. He points out that the caverns in question belong 

 to the Jurassic formation : apparently intending to imply that 

 they have an antiquity related to that of the formation. But 

 there is no such relation, except that the caverns cannot be older 

 than the formation. They may have originated at any period 

 since the containing strata were deposited ; and they may be 

 therefore relatively modern. But passing over this, and admit- 

 ting that the Proteus has inhabited the caverns for an enormous 

 period, what is to be said of the fact that their eyes have not 

 disappeared entirely, as Prof. Weismann contends they should 

 have done had the inheritance of the effects of disuse been all 

 along operative ? There is a very sufficient answer — the rudi- 

 mentary eyes are not entirely useless. It seems that when the 



* Essays upon Heredity^ p. 87. 



