Chapter VII

PROOFS FROM EMBRYOLOGY, OR COMPARISON IN THE ONTOGENIC SERIES.

_Resemblance of the three series_--Frog, in Ontogeny passes
through main stages of Taxonomy and Phylogeny--Resemblance
only general--Many steps dropped out in Ontogeny 148

(1) _Ontogeny of tailless amphibians_--The frog: fish stage,
perennibranch stage, caducibranch stage, aneural stage--Same
stages in Phylogeny 150

(2) _Aortic arches_--Those of lizard described--Origin from
gill-arches of fish--Change from one to the other in Ontogeny
of a frog--Same changes in Phylogeny of lizard--Embryonic
condition of mammalian heart and vessels--Gradual change and
final condition in birds--In mammals--Gradual decrease in
number of aortic arches as we go up the vertebrate scale--
Cogency of the argument from aortic arches 151

(3) _Vertebrate brain_--Fish brain--Brain of reptiles, birds,
mammals, man compared--Human brain passes through similar
stages--Changes in complexity of structure in Taxonomy--
Same changes in Ontogeny of mammals--Same in Phylogeny of
reptiles, birds, mammals 162

_Cephalization_--Explanation of, in body, in mind 171

(4) _Fish-tails_--Homocercal and heterocercal--Vertebrated
and non-vertebrated--Order of change in Ontogeny--Same
in Phylogeny--Similar changes in birds’ tails in Ontogeny
and Phylogeny--In other tailless animals--Examples from
articulates, insects, crustaceans, etc. 172

_Illustration of the differentiation of the whole animal kingdom_
--Development of eggs of all kinds of animals--This a type
of changes in Phylogeny--Why Ontogeny repeats Phylogeny--
Law of acceleration 176

_Proofs from rudimentary and useless organs_--Examples from
whale: Teeth--Limbs--Hair--Olfactive organs--Examples
from man: muscles, cæcal appendage--Significance of useless
organs 179