The daily worker. [volume] (Chicago, Ill.) 1924-1958, 1926-09-03
Ernst HaeCkGI
on last Words
on Evolution"
CHAPTER II.
THE STRUGGLE OVER OUR GEN.
EALoGIcAL TREE.
Our Ape-ReIatlves and the Vertebrate
49, Stem.
CONTINUED from previous issue.)
cHApTEp n

But, important as these arguments
of comparative embryology are, one
needs many years study in the unfa-
miliar and difficult province of EN-
bryology before one can realize their
evolutionary force. There are, in fact,
not a few embFyologists Especially of
the modern school of experimental en-
bryology) who do not succeed in do
ing so. 1t is otherwise with the pal
pable proofs that we take from a re-
mote science, paleontology. The re-
markable fossil remains sand impress
sions of extinct animals and plants
give us directly the historical evil
dence we need to understand the sue.
cessiye appearance and disappearance
of the various species and groups.
Geology has firmly established the
chronological order of the sedimentary
rocks, which have been successfully
formed of mud at the floor of the
ocean, and has deduced their age from
the thickness of the strata, and deter
mined the relative date of their for.
nation. The vast period during which
Va 60AAS A1AC Aelo DCC4 uEFCAODiuh OA
the earth runs to many million years.
The number is variously estimated at
less than hundred or at several hum
bred million years" If we take the
smaller number of 200 million years,
we find them distributed amongst the
Eve chief periods OF the earths or
ganic development in such a way that
the earlier or archeozoic period abb
serbs nearly one-half. As the sedi.
mentary rocks Of this period, chiefly
kneisses and crystalline schists, are in
metamorphosed condition, the fos-
| SD remains In them are unrecogniH-
able. In the next succeeding strata Of
the paleozoic period we find the ear
Hest remains of fossilized vertebrates,
Silurian primitive fishes (selachi) and
gaaoids. These are followed, in the
Devonian system, by the first dip
neust fishes "a transitional form from
the fishes to the amphibia). In the
next. the Carboniferous system, we
find the first terrestrial or four-footed
NEUTRALITY-SUSPICIOUS. Of the order
. of the stegocephala. A little later, IN
the Permian rocks, the earliest am
NOTES. lowly, lizard-like reptiles Ito
| cosauria) make their appearance; the
warm-blooded birds and mammals are
still wanting. We have the first traces
Of the mammals in the Triassic. the
earliest sedimentary rocks OF the
mesozoic age; these are OF the mono
IRENE sub-class Cpantotheria and Allo-
theria). They are succeeded by the
first marsupials (prodidelphia) in the
Jurassic, the ancestral forms Of the
| placentals (mallotheria), in the Gre
! taceous. See p 165.
But. the richest development Of the
mammal class takes place in the next
or Tertiary age. In the course Of its
four periods-the eocene, oligocene,
and pliocene-the mammal species in
crease steadily in number, variety and
completely, down to the present time.
From the lowest common ancestral
group Of the placentals proceed our
divergent branches, the legions OF the
carnassia, rodents, ungu1ates. and
primates. The primate legion sur
poboCS OH lnC ACbAr III IulS 1Lllu6 lOuk
ago included the lemurs, apes, and
man. The historical order in which
the various stages OF vertebrate de-
velopment make their successive ap-
pearance corresponds entirely to the
morphological order of their advance
in organization, as we have learned
it from the study of comparative anat
omy and embryology.
In his presidential speech Of the
last meeting of the British Associa-
ton, Professor Darwin said: 1T does
not seem unreasonable to suppose that
500 to 1000 million years may have
elapsed since the birth of the moon"
| QTrans.l
ITO be continued.)
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