organs; but that the effects
of use and disuse have often been largely combined with, and sometimes
overmastered by the natural selection of innate variations.

_Correlation of Growth._--I mean by this expression that the whole
organisation is so tied together during its growth and development, that
when slight variations in any one part occur, and are accumulated through
natural selection, other parts become modified. This is a very important
subject, most imperfectly understood. The most obvious case is, that
modifications accumulated solely for the good of the young or larva, will,
it may safely be concluded, affect the structure of the adult; in the same
manner as any malconformation affecting the early embryo, seriously affects
the whole organisation of the adult. The several parts of the body which
are homologous, and which, at an early embryonic period, are alike, seem
liable to vary in an allied manner: we see this in the right and left sides
of the body varying in the same manner; in the front and hind legs, and
even in the jaws and limbs, varying together, for the lower jaw is believed
to be homologous with the limbs. These tendencies, I do not doubt, may be
mastered more or less completely by natural selection: thus a family of
stags once existed with an antler only on one side; and if this had been of
any great use to the breed it might probably have been rendered permanent
by natural selection.

Homologous parts, as has been remarked by some authors, tend to cohere;
this is often seen in monstrous plants; and nothing is more common than the
union of homologous parts in normal structures, as the union of {144} the
petals of the corolla into a tube. Hard parts seem to affect the form of
adjoining soft parts; it is believed by some authors that the diversity in
the shape of the pelvis in birds causes the remarkable diversity in the
shape of their kidneys. Others believe that the shape of the pelvis in the
human mother influences by pressure the shape of the head of the child. In
snakes, according to Schlegel, the shape of the body and the manner of
swallowing determine the position of several of the most important viscera.

The nature of the bond of correlation is very frequently quite obscure. M.
Is. Geoffroy St. Hilaire has forcibly remarked, that certain
malconformations very frequently, and that others rarely coexist, without
our being able to assign any reason. What can be more singular than the
rel