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 
