EVOLUTIONS OF ORGANIZATION. 19 



precisely the same defect as the Lamarckian doc- 

 trine of appetency, only to a greater degree; it 

 does not account for the formation of any new 

 organ, nor for new organs appearing symmetrically. 

 No doubt, on the *'je congois" principle it may be 

 made to lengthen and strengthen to any extent 

 any number of structures already existing, and, 

 potent for degeneration also, may be supposed to 

 dwarf others, when they become incumbrances. 

 Thus it is noticeable that in the series of forms 

 preceding the limbs of the horse, a story on which 

 so much is sometimes founded, no new structure 

 makes its appearance ; simply the third digits have 

 enlarged in size, while those on each side have 

 become smaller; and in the horse of the present 

 day both the enlargement and the dwindling have 

 reached a degree beyond which it is difficult to 

 conceive them passing. I notice these circum- 

 stances though I am not prepared to dogmatize to 

 the effect that it actually was by the sole agency 

 of natural selection that the series of limb-forms 

 alluded to found an appropriate completion in the 

 horse. But that natural selection should give rise 

 to totally new and symmetrical organs is hard to 

 imagine and impossible to prove. Mr. Darwin, to 

 a certain extent, acknowledged the difficulty, and 

 boldly he launched an attempt to account for the 



