, 1873-06-29

inat ls, nshen reptiles, birds, and mammals
may BE- subdiyided according to details Of strnc.
ture by which they stand relatively heher ~
lower This series OF rank, determined unon
relative c3nplicasion oi structure is rec57nized
, oy AZ biologists. and ia, hare shown nnt :.
simple series, but involves endlcsa minor series:
oaaeu II tho saEae way upon structural cberar
ters: @NA1Ao
GRADUATION OF RANK. PAnALIrLEp IN GROWTH
In what have called series OF rank or crada-
ton allude only to animals in the adult confi
co'1;uS LUZ 1t;aaihS as standard of comparison tho
but VIC have so1uelhing Of the same kind in tho
series determined by growth; that is, bv tho
changes which animals. undergo. from tho time
"nen the whole mass Of substance is nothing but
IN accumulation Of yolk coils, presently combin-
ing to form the germ layer reating on the yolk,
anu successlvely passing through phases which
deveiop the outline Of new being and finally
lead to the formation Of u perfect. full grown,
living animal There is, as We have seen, mode
Of development in each type which may be
looked npon as unit. All Radiates, all
MolluHks, all Articulatos, all Vertebrates,
are developed ouch within its own
typo, according to given pattern Of growth,
ordinal features, family features, make their
appearance, they show only typical char.ctera-
that ls, what belongs to them as members of
! their type, but not what charactorizes them as
members Of any particular group within that
type. But within each such general series Of
| growth are minor series, determining special
cha1actsE:zsics. The Vertobrates have q mode
OF development peculiar to themselves, and 80
similar that, aa we have seen, it is difficult to
distinguish the human embryo from that Of
any quadruped. But within that genernl Var-
1epiate series Of growth, We have minor and
| nor more special series; those upon which the dog,
yertebrates ire developed. So e in Il thss sAbn blds:
| their growth as whole reminds us often OF the
quadEE1ped strikingly; but they have their un-
] gal1anle and unfairly specific modes Of growth
II ~A rocfsr In1n h.
some particular group Of birds. In those ami
| 1nala whose ombryology has been carefully
studied, the Investigator is not misled by general
fesemolences, for we can anticipate the final ro-
and In each the aki1lful embryologist re-
cognizes the peculiarlties which are tic pro-
cursors OF the ultimate complication Of struc-
ture. Looking upon all these series of Verte-
We look upon the type Of adult Vertebrate, IS
whole, We SEQ both sets Of phenomena as
single pictures; all the minor so1ies OF
rank and growth melting into one simple seriea
both IN this comprehensive way, We, can. fairly |
compare them. There is q time when the human |
embroyo is 80 like the fish e1nbroyo that it is |
ha-d to say what is specifically human and what I
the reptile and to the bird and its OWN char
acteristics are superinduced upon those which it
has IN common with the lower representations
OF the type. Such = series Of growth, corres-
have among Vertebrates, among Articu1ates,
among Mo1usks, and among Radiates. II you
will carefully compare it's different phases Of de-
ve1opment, yon., will find that an insect during
first the lowest Articu1ates, the worm, in its
caterpillar condition; then the crustaceA in it's
chrysain state, and only takes on ita insect
features whon it is full grown.
GENERAL FACTS As 10 STRUCTURAL GRADA11oN.
In certain sense the structural history of
every individual member Of the highest class in
any type may be said to be the structural history
OF the whole type. It is q little mora 1e6ible to
the common observer in the Articulates than in
any other type, because the highest class under
goes it's growth Dc the distinct chapters OF con-
nected metamorphosis; but it is equally true for
AL u had time could show jou in detail
ing in the tn egg, have, first, polyp-hke, then
folturos, and that whom thoy finally
assume the characteristics Of their clasa
(supposing that they belong to the higher spe-
of the lower families before they attain their
oWn specific features. In short, We may say
that the classes within every type, the orders
within every class, the families within every or
der, tho genera within every family, and the
species within each genus, present structural
s7adation more or less marked. The embryol-
ogy Of the higher animals in each type helps us
o understand this graduation BY showing it to US
Q say that auy embfyology corresponds il
III its details to the structural relations
II full grown animals. But when ne find
hat q r5ptile is dsh-liko before it as
I'D quadrupeds are 1sh snd rcptile-like be-
ore they develop their class features and that
wen the human embryo passes through phases
esembing Ill these lower groups, We may be
aDged them before we knew their embryology
) the correct one since their mode OF develop
1ent confirms it. The same kind of core
peondeuce prevails between embryological de-
sh were the first vertebrates introduced upon
arth: Then came the great reptiles, then birds,
nd latest, mammals, quadrupeds, and man.
'e do not yet knox how fa9 these cor
Psp0Pssn'os nos faiaS Nth the em55ooF be5
i history Of great many animals
ut SO far AZ science has gone in this kind Of
lvest;gation, the results are everywhere the
.me. Take, for instance, tho Echinoderms;
10 earliest representatives Of that class Of
adiatea were the Crinoids (ssar-fshes on stems)
OF, the Echinoderms Of the present day pass
rough q distinct crinoida1 phase Of develop
ent, and I may add that there is among the
:esent Echioderms lower group, the members ~
which ere always attached to stem (the '"
entacrinus and similar genera), 30 that in this
stance the series Of geological succession Of
nix among the living agree remarkably. tn
u1d give you various instances Of the same &c
nd but all these facts belong proper ri
to my course on geological succession ~ ~
III pAlAou1OloEJ, Ae4t teILl, AuQ eQ0ulQ cnlY -
MUSE your minds did attempt to present tn
em now. only bring forward enough to show eY en-
is basis for the ardent discussion going on Gu
nong naturalists during the last ten Or Twelve str
ars as to the real nature of these relations, tn
,e ovolutionists, as I have shown you in the MI
tracts With which have opened this lecture g1'
9 the parallelism between the senes Of ombry- Pc!
ic growth aud geological succession as sup ;.
ring their theory. But eyen were the pnral- etr
ism complete they would have it, the eyi- N
nee is vitiatod By the fact that it extsnds to da
les OF rank among living animals. and. "A Bpe
I'D show vbu also to a terie. of the sama We
ID controlling the geographical distribution OF 1a 1as
mails. toH
Int aver xrc7. +ha co,reanonda,c. .o,,+nod boy
successive appearance OF animals ip time, XII XII
- soo-no 5as,dpn.s ~ ~ e". uoeo ~ aWs
a@,s1 ax-isna+;oo ~ 10 1e"a ~ 6..9 ~ 4uJ by
sa..t d;gars;t- sna,1 40 a,,insa1a ~ "1n w ful
In So n.u@ .e M o ~ "A1 p1ou8nE and