n the foot of a horse, place us in a dilemma. For,
either these rudiments are of no use to the animal, in which case,
considering that the horse has existed in its present form since the
Pliocene epoch, they surely ought to have disappeared; or they are of
some use to the animal, in which case they are of no use as arguments
against Teleology. A similar, but still stronger, argument may be
based upon the existence of teats, and even functional mammary glands,
in male mammals. Numerous cases of "Gynaecomasty," or functionally
active breasts in men, are on record, though there is no mammalian
species whatever in which the male normally suckles the young. Thus,
there can be little doubt that the mammary gland was as apparently
useless in the remotest male mammalian ancestor of man as in living
men, and yet it has not disappeared. Is it then still profitable
to the male organism to retain it? Possibly; but in that case its
dysteleological value is gone.

II. Professor Haeckel looks upon the causes which have led to the
present diversity of living nature as twofold. Living matter, he tells
us, is urged by two impulses: a centripetal, which tends to preserve
and transmit the specific form, and which he identifies with heredity;
and a centrifugal, which results from the tendency of external
conditions to modify the organism and effect its adaptation to
themselves. The internal impulse is conservative, and tends to the
preservation of specific, or individual, form; the external impulse is
metamorphic, and tends to the modification of specific, or individual,
form.

In developing his views upon this subject, Professor Haeckel
introduces qualifications which disarm some of the criticisms I should
have been disposed to offer; but I think that his method of stating
the case has the inconvenience of tending to leave out of sight
the important fact--which is a cardinal point in the Darwinian
hypothesis--that the tendency to vary, in a given organism, may have
nothing to do with the external conditions to which that individual
organism is exposed, but may depend wholly upon internal conditions.
No one, I imagine, would dream of seeking in the direct influence of
the external conditions of his life for the cause of the development
of the sixth finger and toe in the famous Maltese.

I conceive that both hereditary transmission and adaptation need to be
analysed into their constituent conditions by the further application
of the doct