The T: heory of Evolution oe 
group identical; for with a sufficient knowledge of the devel- 
opment it is always possible to distinguish between the em- 
bryos of different species, as well as between the adults, only 
it is more difficult to do so, because the embryonic forms are 
simpler. The most fundamental difference between the view 
of Von Baer and modern views is due to our acceptation of 
the theory of evolution which seems to make it possible to 
get a deeper insight into the meaning of the repetition, that 
carries us far ahead of Von Baer’s position. For with the 
acceptance of this doctrine we have an interpretation of how 
it is possible for the embryonic stages of most members of a 
group to have the same form, although they are not identi- 
cal. There has been a continuous, although divergent, stream 
of living material, carrying along with it the substance out of 
which the similar embryonic forms are made. As the stream 
of embryonic material divided into different paths it has also 
changed many of the details, sometimes even all; but never- 
theless it has often retained the same general method of 
development that is associated with its particular composition. 
We find the likeness, in the sense of similarity of plan, ac- 
counted for by the inheritance of the same sort of substance ; 
the differences in the development must be accounted for in 
some other way. 
Among modern writers Hurst alone has advanced a view 
that is similar in several respects to that which I have here 
defended. It may be well to give his statement, since it 
brings out certain points of resemblance with, as well as cer- 
tain differences from, my own view.' He says: “ Direct 
observation has shown that, when an animal species varies 
(z.e. becomes unlike what it was before) in adult structure, 
those stages in the development which are nearest the adult 
undergo a similar, but usually smaller, change. This is shown 
in domestic species by the observations of Darwin, and the 
1 Hurst, C. H., “Biological Theories, III,” “The Recapitulation Theory,” 
Natural Science, Vol. ii., 1893. 
