closely resembles that of De Maillet, made a great advance upon the
crude and merely speculative manner in which that writer deals with the
question of the origin of living beings, by endeavouring to find
physical causes competent to effect that change of one species into
another, which De Maillet had only supposed to occur. And Lamarck
conceived that he had found in Nature such causes, amply sufficient for
the purpose in view. It is a physiological fact, he says, that organs
are increased in size by action, atrophied by inaction; it is another
physiological fact that modifications produced are transmissible to
offspring. Change the actions of an animal, therefore, and you will
change its structure, by increasing the development of the parts newly
brought into use and by the diminution of those less used; but by
altering the circumstances which surround it you will alter its actions,
and hence, in the long run, change of circumstance must produce change
of organization. All the species of animals, therefore, are, in
Lamarck's view, the result of the indirect action of changes of
circumstance upon those primitive germs which he considered to have
originally arisen, by spontaneous generation, within the waters of the
globe. It is curious, however, that Lamarck should insist so
strongly[64] as he has done, that circumstances never in any degree
directly modify the form or the organization of animals, but only
operate by changing their wants and consequently their actions; for he
thereby brings upon himself the obvious question, how, then, do plants,
which cannot be said to have wants or actions, become modified? To this
he replies, that they are modified by the changes in their nutritive
processes, which are effected by changing circumstances; and it does not
seem to have occurred to him that such changes might be as well supposed
to take place among animals.

When we have said that Lamarck felt that mere speculation was not the
way to arrive at the origin of species, but that it was necessary, in
order to the establishment of any sound theory on the subject, to
discover by observation or otherwise, some _vera causa_, competent to
give rise to them; that he affirmed the true order of classification to
coincide with the order of their development one from another; that he
insisted on the necessity of allowing sufficient time, very strongly;
and that all the varieties of instinct and reason were traced back by
him to the sam