arine. Now is it possible to conceive external
conditions more closely alike than those to which the buds on the same tree
are exposed? Yet one bud alone, out of the many thousands borne by the same
tree, has suddenly without any apparent cause produced a nectarine. But the
case is even stronger than this, for the same flower-bud has yielded a
fruit, one-half or one-quarter a nectarine, and the other half or
three-quarters a peach. Again, seven or eight varieties of the peach have
yielded by bud-variation nectarines: the nectarines thus produced, no
doubt, differ a little from each other; but still they are nectarines. Of
course there must be some cause, internal or external, to excite the
peach-bud to change its nature; but I cannot imagine a class of facts
better adapted to force on our minds the conviction that what we call the
external conditions of life are quite insignificant in {289} relation to
any particular variation, in comparison with the organisation or
constitution of the being which varies.

It is known from the labours of Geoffroy St. Hilaire, and recently from
those of Dareste and others, that eggs of the fowl, if shaken, placed
upright, perforated, covered in part with varnish, &c., produce monstrous
chickens. Now these monstrosities may be said to be directly caused by such
unnatural conditions, but the modifications thus induced are not of a
definite nature. An excellent observer, M. Camille Dareste,[712] remarks
"that the various species of monstrosities are not determined by specific
causes; the external agencies which modify the development of the embryo
act solely in causing a perturbation--a perversion in the normal course of
development." He compares the result to what we see in illness: a sudden
chill, for instance, affects one individual alone out of many, causing
either a cold, or sore-throat, rheumatism, or inflammation of the lungs or
pleura. Contagious matter acts in an analogous manner.[713] We may take a
still more specific instance: seven pigeons were struck by
rattle-snakes;[714] some suffered from convulsions; some had their blood
coagulated, in others it was perfectly fluid; some showed ecchymosed spots
on the heart, others on the intestines, &c.; others again showed no visible
lesion in any organ. It is well known that excess in drinking causes
different diseases in different men; but men living under a cold and
tropical climate are differently affected:[715] and in this case we see