Paris. Lastly, it is well
known that caterpillars fed on different food sometimes either
themselves acquire a different colour or produce moths different in
colour.[699]

{281}

It would be travelling beyond my proper limits here to discuss how far
organic beings in a state of nature are definitely modified by changed
conditions. In my 'Origin of Species' I have given a brief abstract of
the facts bearing on this point, and have shown the influence of light
on the colours of birds, and of residence near the sea on the lurid
tints of insects, and on the succulency of plants. Mr. Herbert
Spencer[700] has recently discussed with much ability this whole
subject on broad and general grounds. He argues, for instance, that
with all animals the external and internal tissues are differently
acted on by the surrounding conditions, and they invariably differ in
intimate structure. So again the upper and lower surfaces of true
leaves, as well as of stems and petioles, when these assume the
function and occupy the position of leaves, are differently
circumstanced with respect to light, &c., and apparently in consequence
differ in structure. But, as Mr. Herbert Spencer admits, it is most
difficult in all such cases to distinguish between the effects of the
definite action of physical conditions and the accumulation through
natural selection of inherited variations which are serviceable to the
organism, and which have arisen independently of the definite action of
these conditions.

Although we are not here concerned with organic beings in a state of
nature, yet I may call attention to one case. Mr. Meehan,[701] in a
remarkable paper, compares twenty-nine kinds of American trees, belonging
to various orders, with their nearest European allies, all grown in close
proximity in the same garden and under as nearly as possible the same
conditions. In the American species Mr. Meehan finds, with the rarest
exceptions, that the leaves fall earlier in the season, and assume before
falling a brighter tint; that they are less deeply toothed or serrated;
that the buds are smaller; that the trees are more diffuse in growth and
have fewer branchlets; and, lastly, that the seeds are smaller--all in
comparison with the corresponding European species. Now, considering that
these trees belong to distinct orders, it is out of the question that the
peculia