THE ARGUMENTS FROM EMBRYOLOGY. 379 



ticular organs, must obscure the embryologic history. And 

 the parts influencing the whole in degrees varying with their 

 masses, there results a further influence which, from the out- 

 set, must begin to modify the metamorphoses of each kind of 

 embryo ; and cause it to show incipient divergences from 

 embryos which had ancestral histories the same as its own. 

 Thus we find three different causes conspiring in endless 

 ways and degrees, to produce deviations from the general law 

 — causes which are manifestly capable of producing, under 

 special conditions, changes in apparent contradiction to this 

 law. 



