Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-01-27
Tracing Lies Pathway

1t is not infrequent deformity in cats
and cattle, and probably in other ver-
| tebrateS; but in these it only appears
occasionally and the individuals so
uniformed usually die young. being I'M
| able to meet the competition of their
relatives of the usual type.
study of the malformed young of
cats and cattle shows that in these
animals there Is latent tendency to
develop types with the same build as
the rabbit or the kangaroo. A kan
garoo-ltke cat. however, could not hold
its prey, while the feet of a Kangaroo
like COW would be wholly unsuited to a
leaping mode of progress. Nature con-
stantiy is striving to produce these
creatures which in the modern world
are impossible anomalies.
Among the butterflies and moths in
dividualS occasionally are found which
are male on one side and female on the
other. Sometimes the wings of a single
individual are divided into regular or
more or less irregular patches some of
which show the male and others the
female, type of coloration. Many in
stances Of hermaphroditiSm are also
known from other insects and from all
the groups of vertebrates.
Such biseXualism is a characteristic
features of all the individuals in
number of different types of animals
where its fixation as normal feature
is not incompatible with other econo-
mically necessary features.
Summing up the statements made
above, we find that a satisfactory theory
of evolution must explain a certain cor
respondence indicated, but not yet
worked out in detail. between the or
ganic and the inorganic worlds; the
curious correspondence in all the broad
er features between the very earliest
fossils and the living animals, and the
occurrence of gaps of all degrees be-
tween the different sorts of animals.
It is not concerned with the explana-
ton OF the excess of different animal
types occurring in the sea.
Evolutionary Tree Picture.
Clearly three requirements cannot be
met by a single straight evolutionary
line. Neither will the usual figure of
an evolutionary tree with numerous
branches leading nowhere serve the pur-
pose. The numerous gaps, often very
broad between the animal types renders
straight line. or branching tree-like
figure, quite inadequate to portray the
truth.
Within restricted groups there might
be shown an evolutionary line, broken
at intervals and more or less devious
IN direction. or even sketchy tree
like figure, that would approximate the
truth. But for animals as a whole
some other scheme is necessary.
A study Of the development of ami
mails points out the way to such a
scneme. All animals originate from
CfnUtn
hves as single cells, while in others the
original single cells divide and become
more or less complex mass of cells.
Assuming that the earliest animals.
IKE those of the present day, began
lie as a single cell, there are three
alternatives which subsequent develop
ment might follow. There is no reason
1or believing that these three paths
We're not followed simultaneously-tha
Is, tnat animal life did not from the
nrst develop in three divergent WAYS.
AS the original cells divide the re-
Suitant cells may separate from each
other so that the individual animals
always remain composed of a single cell
In other words, on the division into
TWO OF the original cell, each half NAV
separate from the other and become q
separate animal half the size of the
original, Further division would give
rise 10 corresponding number of en-
tlrely separate animals, all when thew
reach the maximum size increasing nv
simple division into two The so-called
protozoans or Single-celled animals Ill
lustrate this process.
Cells i'm Contact.
But after division into two the cells
might remain in contact and this CON
tact might be maintained through suc-
cesSive cell divisions. Here there are
TWO alternatives. The cells NAV adhere
more or less irregularly so that a poorly
differentiated mass of cells results the
mass as whole being more or less
distinctly radial in symmetry. The
result OF such development is illustrated
by the sponges.
On the other hand, cell division NAV
TAKE place by regular geometrical
progression, the original cell dividing
nIo 2, 4, 10, 81, ga, and so on, until q
noHoW pan or cells, known as blastula.
Is formed, which. by collapsing. would
10TH a two-layered cup, known as
the center of the opening and of the
opposite pole, and the walls the same
In all the radii.
such an animal form should con-
tinue Its development to the adult
stage, following to its logical conclusion
the preceding line of geometrical de-
Veiopment, the result would be an
animal radially symmetrical and cow
posed OF two layers of cells. such an
animal is represented by the HYDRA. the
sea-anemone. and the very numerous
allied creatures.
MOST significant is the fact that every
animal, excepting for those lust men
Toned, mas a gaStrula or hydra stage
IN lts development. But at this STAGE
Sonetning goes wrong with the radial
ueveIopment, and later development
gives rise TO creature with a head end
at which sense organs are develonad
and to which the mouth mierates
Groups of Animals.
Ihere are four great groups of
animals which retain, to a large extent
evidences of the fundamental radial
symmetry, yet are to an equal, or even
greater, extent, bilaterally symmetrical.
with more or less indefinite head.
betWeen each two of these four
groups is another animal group COM
nlnlng the characters of those on
eIIner side, though widely different
from them. Within this inner circle
are four others, bearing the Same re1a-
ZION TO them that they do to the first
Tour. Three other circlets of four
groups. each arranged in the same wav.
complete the picture, and in the center
stand the vertebrates or back-boned
ANIMALS. Unfortunately the names of
THESE various groups are without mean
ing save to BIOLOGISTS.
by this arrangement of the numerous
ol1erent types of animals we get a
1 T place Tor each and every group.
! Each is sharply cut off from ali the
rest as If the major types of animals
were recrystallization of features in
herent in animals as a whole. Such a
diagram brings this out.
In such plan of evolution no time
element is involved, and there is no
reason .a Tor assuming that any of the
mA1lr If