78 ADAM SEDGWICK. 



others, that the embryo dogfish differs from the embryo chick, 

 I am quite aware that arguments tending to reduce the 

 classificatory value of the embryonic differences I have just 

 enumerated might with more or less plausibility be adduced. 

 But one thing at a time. I am at present dealing solely with 

 the importance of the anatomical resemblances and differences 

 between the embryos ; and I think I have shown, as far as it 

 can be shown, that they have, if judged by standards used 

 when comparing adults, at least as great an importance as the 

 resemblances between the same embryos — the differences, like 

 the resemblances, relating solely to the embryos, and not 

 existing in the adults. V. Baer's law then falls to the ground, 

 and must be replaced by another law, which is as follows : — 

 Embryos of different members of the same group often resemble 

 one another in points in which the adults differ, and differ from 

 one another in points in which the adults resemble ; and it is 

 difficult, even if possible, to say whether the differences or the 

 resemblances have the greater zoological value (because we 

 have no clearly defined standard of zoological value). 



It will probably be urged here by my reader — Are you not 

 beating the air in a vain warfare of words and unessentials of 

 which we were all aware, and trying to kick up a cloud of dust 

 by which to obscure the essential point, viz. that embryos 

 pass through, incompletely if you like, stages of structure 

 permanent in lower members of the same group? To such a one 

 I reply, that I am as keenly alive to the importance of the 

 essential point as he is, but that I differ from him in being 

 dissatisfied with the explanation which is at present given of it, 

 and that I am convinced that the form in which this pheno- 

 menon is referred to in v. Baer's law has led to the acceptance 

 of an imperfect explanation of the embryonic phase in animal 

 development. 



(2) But before I come to that point I have to consider 

 the case of the embryos of closely allied animals. If v. 

 Baer's law has any meaning at all, surely it must imply that 

 animals so closely allied as the fowl and duek would be indis- 

 tinguishable in the early stages of development ; and that iu 



