and did not
trouble about its mode of origin. They held indeed that form-production
was due to a complex of physico-chemical causes, which they hoped some
day to unravel;[464] but this future physiology of development remained
quite embryonic.

Physiology then had not really come into contact with the problems of
form, and it could give the morphologist no direct help when he turned
to investigate the causes of form-production. It had, however, a
determining influence upon the methods of those who first broke ground
in this No Man's Land between morphology proper and physiology. But it
is significant that it was a morphologist and not a physiologist that
did the first spade-work.

The pioneer in this field, both as investigator and as thinker, was W.
Roux, who sketched in the 'eighties the main outlines of a new science
of causal morphology, to which he gave the name of
_Entwicklungsmechanik_. The choice of name was deliberate, and the word
implied, first, that the new science was essentially an investigation of
the development of form, not of the mode of action of a formed
mechanism, and second, that the methods to be adopted were
mechanistic.[465]

Though Roux was the only begetter of the science of
_Entwicklungsmechanik_, he was, of course, not the first to investigate
experimentally the formative processes of animal life. Study of
regeneration dates back to Trembley (1740-44), Reaumur (1742), Bonnet
(1745), and Spallanzani (1768-82),[466] and in the years preceding Roux's
activity good work was done by Philipeaux. A beginning had been made
with experimental teratology by E. Geoffroy St Hilaire and others, and
the work of C. Dareste[467] remains classical. Back in the 18th century,
some of John Hunter's experiments had a bearing upon the problems of
form; his work on transplantation was followed up in the 19th century by
Flourens, P. Bert, Ollier and many others. In founding in 1872 the
_Archives de Zoologie experimentale et generale_ H. de Lacaze-Duthiers
put forward in his introduction a powerful plea for the use of the
experimental method in zoology.

In some ways more directly connected with _Entwicklungsmechanik_ was
His's attempt in 1874[468] to explain on mechanical principles the
formation of certain of the embryonic organs by the bendings and
foldings of tubes or plates of cells. "His compared the various layers
of the chick embryo to elastic plates and tubes; out of these he
suggested that some of th