50 EVOLUTION 



their embryonic stages. They seem, as it 

 were, to travel for a considerable distance 

 along the same road, or along closely parallel 

 roads, before they diverge, each on its own 

 path of development. 



It is only in a very general way that we can 

 accept the late Professor Milnes Marshall's 

 epigram, that the individual climbs up its 

 own genealogical tree; yet there is no doubt 

 that the development of the individual is in 

 some measure interpretable as a condensed 

 recapitulation of the presumed racial evolu- 

 tion. There is no doubt that in many cases 

 the developing embryo pursues a strangely 

 circuitous path instead of progressing straight 

 towards its goal, and the only light that we 

 can throw on many instances of this circuitous- 

 ness when it is not adaptive to the peculiar 

 conditions of development is the light from 

 the past. The living hand of the past is upon 

 the embryo, constraining it to follow the old 

 route of its race, and often reasserting its 

 power in trivial details, even when a consider- 

 able short-cut has been made. 



Thus in the development of every reptile, 

 bird and mammal there are residues of gill- 

 clefts, sometimes imperfectly opening, which 

 have no respiratory significance whatsoever, 

 which can hardly be said to be of any use at 



