THE BIOGENETIC LAW 189 



would suffer. Thus at first only those determinants may disappear — 

 and can disappear according to the laws of germinal selection — which 

 control the final form of the useless organ, then those just preceding 

 them, which controlled, let us say, its size, and thus more and more of 

 the previously active determinants disappear, and hand in hand with 

 this disappearance there is variation of all the parts correlated with 

 the dwindling condition of the organ, so that their own development 

 and that of the animal as a whole suffers no injury. If it were 

 otherwise, if when a part became useless its collective determinants 

 were all to disappear at the same time, the whole ontogeny would 

 totter, in fact it would be much as if a man who wished to remove 

 the breadth of a window from a house standing on pillars were to 

 begin by taking away the foundation pillar. 



It is, of course, to be understood that these processes go on so 

 exceedingly slowly that personal selection takes a share in them, at 

 least at the beginning. Later on, the further degeneration of a useless 

 organ or rudiment has no effect on the individual's power of life, and 

 therefore depends solely upon the struggle of the parts within the 

 germ-plasm (germinal selection). 



If we could see the determinants, and recognize directly their 

 arrangement in the germ-plasm and their importance in ontogeny, we 

 should doubtless understand many of the phenomena of ontogeny and 

 their relation to phylogeny which must otherwise remain a riddle, or 

 demand accessory hypotheses for their interpretation. Several years 

 ago Emery rightly pointed out that the phenomena of the variation 

 of homologous parts might be inferred by reasoning from the germ- 

 plasm theory. If one hand has six fingers instead of five, it not 

 infrequently happens that the other also exhibits a superfluity of 

 fingers, and sometimes the foot does so too. The phyletic modification 

 of the limbs in the Ungulates has taken place with striking uniformity 

 in the fore and hind extremities ; no animal has ever been one-hoofed 

 in front and two-hoofed behind. Although I might suggest that this 

 primarily depends on adaptation to different conditions of the ground, 

 and that the Artiodactyls were evolved in relation to the soft marshy 

 soil of the forest, and the Perissodactyls for the steppes, it cannot be 

 denied that germinal conditions may have co-operated in bringing 

 about this uniformity of the direction of variation, especially as the 

 whole structure of the fore- and hind-limbs exhibits such marked 

 similarity. Emery is inclined to refer this to ' germ-plasmic correla- 

 tions,' and we have assumed from the very first that the different 

 determinants and groups of determinants do indeed stand in definite 

 and close relations to one another. But it seems to me premature to 



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