rences between the adults,
but who is prepared to affirm that the presence of a cephalic coelom and
of cranial segments, of external gills, of six gill slits, of the kidney
tubes opening into the muscle-plate coelom, of an enormous yolk-sac, of
a neurenteric canal, and the absence of any trace of an amnion, of an
allantois and of a primitive streak are not morphological facts of as
high an import as those implied by the differences between the adults?
The generalisation undoubtedly had its origin in the fact that there is
what may be called a family resemblance between embryos and larvae, but
this resemblance, which is by no means exact, is largely superficial and
does not extend to anatomical detail.

It is useless to say, as Weismann has stated ("The Evolution Theory",
by A. Weismann, English Translation, Vol. II. page 176, London, 1904.),
that "it cannot be disputed that the rudiments [vestiges his translator
means] of gill-arches and gill-clefts, which are peculiar to one stage
of human ontogeny, give us every ground for concluding that we possessed
fish-like ancestors." The question at issue is: did the pharyngeal
arches and clefts of mammalian embryos ever discharge a branchial
function in an adult ancestor of the mammalia? We cannot therefore,
without begging the question at issue in the grossest manner, apply to
them the terms "gill-arches" and "gill-clefts". That they are homologous
with the "gill-arches" and "gill-clefts" of fishes is true; but there
is no evidence to show that they ever discharged a branchial function.
Until such evidence is forthcoming, it is beside the point to say that
it "cannot be disputed" that they are evidence of a piscine ancestry.

It must, therefore, be admitted that one outcome of the progress of
embryological and palaeontological research for the last 50 years is
negative. The recapitulation theory originated as a deduction from the
evolution theory and as a deduction it still remains.

Let us before leaving the subject apply another test. If the evolution
theory and the recapitulation theory are both true, how is it that
living birds are not only without teeth but have no rudiments of teeth
at any stage of their existence? How is it that the missing digits in
birds and mammals, the missing or reduced limb of snakes and whales, the
reduced mandibulo-hyoid cleft of elasmobranch fishes are not present or
relatively more highly developed in the embryo than in the adult? How
is it