New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1873-06-07
THE FOUR TYPES OF ANIMALS.

CAMBRIDGE, Mass, June O'-lho 'oi'V""o
lecture was delivered by Prof. AgassH beiore 'no i""
scum Of Comparative Zoology. on the go ui'';
ehaye seen in previous lectures that the Vertebraes
and R,oates that is the highest and lowest type OF the
animal kingdom are based upon two plans OF structure
unite distinct from each other You have furIher soen
that each type is gushef NY special mode OF uo
yeopment 10 short these two types are held togeVhe
each within its own limits By structure ana ny CROWN
As to the limits Of the type Invertebrates there IS HUI
dissenting voice among naturalists. FROM tho 'o -
Aristotle to the present day all animals WIN o'oA'
bone have been recognized belonging to them though
Aristotle united them with another character ana caeu
them blood animals" 1t is true that the AmphloNuS
was once referred to the class of worms on account
OF its extreme resemblance 10 thcm' Dut AZ Soou
as the plan OF its internal structure was understoou "
was transferred to the Yertebraes The RadlateS also
are easily crcumscribed upon structural features anu
naturasts differ only upon the relation OF the Echmo
derms starfshes. sea-urchns and HolothurAhs " 'o
iellyhshes and corals. think have shown you that all
the three classes belong together both by structure ana
by mode of Development but, while naturalsts LISA
gree IN separating the highest Of these three cassos
from the two lower, there is no difference OF OPINION ~
10 the limits of each class taken separately, nor as 10
the position OF the Vertebracs as the highest type Vi
the animal kingdom that Of the Radiates as us low"
est type Between these two strongly oontrasted types
stand ty .hors the Molusks and the Artcuates' do
reference to each other and TO the Radates and Ner
brates or il there any evidence Of transition through
them Of the lower forms into the hlgher ones
To answer this question, or rather to nave some
basis for fair discussion Of we must examine the
organic character Of these groups Have they IKE tho
Radiates and the Verebrate distinct plan OF struc-
ure and mode of development Tho fact that there Is
more disagreement among naturaists about
the limit OF these two groups than ABOUT
that OF the others would seem TO show
that they structurally less clearly uenheu'
But believe we shall find upon examination thaV tniS
is only because some representatives OF these groups
are less well known and that, as in the case OF the AM
phioxus, their anatomy and mode of growth when
rightly understood, will explain their true relations
DIVISIONS OF THE ARTICULATEs.
Tho Articulates are divided into three classes In
sects, Crustacea and Worms About the limits OF tho
two first groups naturasts troubled with no doubts
Expressed in general formula or summary the struc
ture OF Arculates consists Of followed cylinder Ill
vided along its length by movable ionted rings ana
having on the sides appendices Onted in the same way
20 servo locomotive organs Whether these rings are
distributed evenly throughout the length OF tue BODY as
in the worm or are sodered together in front to form
shield and left free behind to form movable tail as IN
the lobster and crab. or arc divided into three
distinct regions head chest. and hindbody as
TO the Insect, does not affect the gen
eral plan Of structure This is the same
in all for the presence absence Of wings, the greater
or less number Of locomotive organs or other external
appendages are superficial features; the structural
idea remains the same as it does the Vertebrates,
though the parts which make fin in tho hsh are mOdl
fed to build a wing in the bird and an arm in man.
But although naturalsts agreed upon fundamental
plan of structure fornsects, crustacea, and worms,
there are some worms in which the locomotive
appendages are wanting, and which they
have been disposed TO separate from the
Articuates on this account l do not myself agree
10 this The difference Is one OF complication or sim
picity OF parts not one OF plan; and tho body OF a
worm without external APPENDICES Is just as much a
cylinder built up Of movable rings as that Of worm
furnished with numerous locomotive appendages. And
here embryOlogy comes to our aid. We find that the
mode OF development OF all these animals is the same and
that all arcuates, the highest group, the insects,
pass through embryonic stages in which they have no
developed limbs The truth Is that phase Of life which
is transient for the higher forms Of this type,
10 permanent for tho lower The insects, in.
deed remain in the worm phase for a
shorter or longer time, for were not the caterpillar
known 20 us as only one chapter OF an Insects life,
what should we call 1t but wOrml Not only do the
embryonic phases Of the artculate germ show that all
these animals have common mode Of Development but
the relation OF the embryo 10 the yok leads to the
same conclusion namely that the process OF growth is
unit for the types Of arhcuates their plan Of sruc
ture is unit; that this is true for them in the same
sense as it is true for the Radatcs and the Vertebrates
[ shall not 20 into the details OF this deYel-
Opment but refer you TO the works OF
Rathke Herold, Faddach and Wessmann. Suffice 1t to
say that the yolk taken into the growing Articuate
upon the back This embryonic feature distinguishes
the mode Of growth in the Artcuates from that Of
all other types OF the animal kingdom and it is directly
connected with their organizations; for the contrast Of
parts in an insect is wholly between the upper and
lower sides not between right and left shall pres
emily see TO be the case with MOusks
DIVISIONS OF TIE MoLLUsKs.
The Mollusks are bound together In similar manner
by structural plan and by growth This type consists
also OF three classes the Cephalopoda cuttlehshes,
nau squids and the likel. Gaseropoda 10 which be-
long the unvalve shells, snas sugs Sc and Acephala
biyave shells, oysters, clans, mussels. and the lke)
The body is soft capable OF great contraction and
panson and had time 10 give you the details OF sruc-
ture could easily show you that the essential features
are the same in ALL whatever are the differences In their
external covering. This group is strilnngly distin
gushed from the Radates by the fact tina: batera SYM
mery is seen in its lowest representatives In the
Radaes there contrast parts which may properly
be called above and below, right and left, before and
behind All parts Of the body in Radiate are disposed
symmetrcay around vertical axis; and this is shown
even in the embryo. For after the augmentation IS
over the first disposition OF tue cells is TO arrange them
selves upon the circumference and TO form hollow
sphere within. The molusks, the contrary, instead
Of having their organs diyergng in every direction
from common center have them arranged upon either
side OF longitudinal axis. The mode OF development
IL also peculiar in the mOusks. The absor0s the
whole substance Of the yolk which ia taken IN not upon
the back OF the body in the Artcuates but from the
ventra side.
These four types, Radates, Mollusks. Arculatcs and
Vertebrate distinct in anatomy and growth that
we can reduce the plan and structure and mode OF de-
. oapb a prta fn A
spherical body with symmetrical division OF parts
dlyergng from vertical axis represents any Radiate
soft contractile body, with the parts arranged on
either side Of LONGITUDINAL axis. represents any Mot