80 Evidence from Embryology 



ganization not far removed from that represented by 

 Peripatus. 



Then the anatomical classifier comes with his 

 species and shows us that while each is a distinct en- 

 tity, itself and no other, they can often be arranged 

 in series, and linked together by divergent variants. 

 Sometimes he can make a plausible genealogical tree, 

 and though his critic promptly proceeds to cut it 

 down, this will not continue indefinitely. The possi- 

 bility of making a "natural" classification spells 

 evolution. 



§8. Embryological Evidence. 



The embryologist joins in and shows how the indi- 

 vidual development reads like a condensed recapitu- 

 lation of presumed racial evolution, how the past 

 lives on in the present, how circuitousness in the in- 

 dividual becoming may receive historical interpreta- 

 tion — how, in short, in a general way, the individual 

 animal climbs up its own genealogical tree. 



For some days the embryonic development of a 

 bird is so like that of a reptile that one may think of 

 the two as proceeding along the same (Sauropsidan) 

 highway together, until they come to the parting of 

 the ways, when the reptile goes to the right and the 

 bird to the left (see the Genealogical Tree). It is 

 very striking to take three or four very young em- 

 bryos of mammals that are not nearly related to one 

 another, simply to see how close the resemblance is 

 in the early stages. But microscopic examination of 

 sections of these embryos shows that there is con- 



