38 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 in 
