CHAPTER V. 

 THE ARGUMENTS FROM EMBRYOLOGY. 



128. THERE was briefly set forth in 52, a remarkable 

 induction established by Yon Baer ; who &quot; found that in its 

 earliest stage, every organism has the greatest number of 

 characters in common with all other organisms in their 

 earliest stages ; that at a stage somewhat later, its structure 

 is like the structures displayed at corresponding phases by a 

 less extensive multitude of organisms ; that at each subse 

 quent stage, traits are acquired which successively distin 

 guish the developing embryo from groups of embryos that it 

 previously resembled thus step by step diminishing the 

 class of embryos which it still resembles ; and that thus the 

 class of similar forms is finally narrowed to the species of 

 which it is a member.&quot; Though this generalization is to be 

 taken with qualifications, yet, as an average truth, it may 

 be regarded as beyond question ; and as an average truth, it 

 has a profound significance. 



For if we follow out in thought the implications 

 of this truth if we conceive the germs of all kinds 

 of organisms simultaneously developing ; if after taking 

 their first step together, we imagine at the second step, one 

 half of the vast multitude diverging from the other half; if, 

 at the next step, we mentally watch each of these great 

 assemblages beginning to take two or more routes of 

 development ; if we represent to ourselves this bifurcation 

 simultaneously going on, stage after stage, in all the 



