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1₄o HERBERT SPENCER

societary forms. In 1864 he wrote to G. H. Lewis,
"If anyone says that had von Baer never written
I should not be doing that which I now am, I have
nothing to say to the contrary—I should reply it
is highly probable."

Herbert Spencer spoke of his early recognition of
von Baer's law as one of the moments in his intel-
lectual development. He realised objectively and
vividly that out of an apparently simple and homo-
geneous stage of development, there is developed by
division of labour and other processes, a wondrous
complexity of nervous, muscular, glandular, skeletal,
and connective tissues or organs, as the case may
be. Organic development is not like crystallisation;
it is heteromorphic crystallisation, so to speak. From
a group of apparently similar cells, heterogeneous
tissues and organs are developed. Thus von Baer
as an embryologist gave Spencer as a general evolu-
tionist a concrete basis for the concept of development
which was simmering in his mind.

Von Baefs Law.—It does not appear, however,
that Spencer ever read von Baer's embryological
memoirs, else he might have been less well-satisfied
with summing up individual development as a progress
from homogeneity to heterogeneity. Von Baer was
much more cautious than some of his followers and
expositors, and subsequent research has justified his
caution. The once popular " Recapitulation Doctrine "
that a developing organism " climbs up its own
genealogical tree," that "ontogeny recapitulates
phylogeny," is now seen to be true only in a very
general way, and with many saving clauses. The
gernj is now known as a unified mosaic of ancestral



	1₄o HERBERT SPENCER societary forms. In 1864 he wrote to G. H. Lewis, "If anyone says that had von Baer never written I should not be doing that which I now am, I have nothing to say to the contrary—I should reply it is highly probable." Herbert Spencer spoke of his early recognition of von Baer's law as one of the moments in his intel- lectual development. He realised objectively and vividly that out of an apparently simple and homo- geneous stage of development, there is developed by division of labour and other processes, a wondrous complexity of nervous, muscular, glandular, skeletal, and connective tissues or organs, as the case may be. Organic development is not like crystallisation; it is heteromorphic crystallisation, so to speak. From a group of apparently similar cells, heterogeneous tissues and organs are developed. Thus von Baer as an embryologist gave Spencer as a general evolu- tionist a concrete basis for the concept of development which was simmering in his mind. Von Baefs Law.—It does not appear, however, that Spencer ever read von Baer's embryological memoirs, else he might have been less well-satisfied with summing up individual development as a progress from homogeneity to heterogeneity. Von Baer was much more cautious than some of his followers and expositors, and subsequent research has justified his caution. The once popular " Recapitulation Doctrine " that a developing organism " climbs up its own genealogical tree," that "ontogeny recapitulates phylogeny," is now seen to be true only in a very general way, and with many saving clauses. The gernj is now known as a unified mosaic of ancestral