, 1876-07-29

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two heads which are united summit to
summit, face to face, or jams like, back
to back. But in all these instances, it is
now thought by the greater number OF
competent judges that the homoiogus
parts are not mutually attractive, hut
that "us union takes place before the
I differentiation of distinct organs occurs,
these ~ merely formed in continuity with
each other 1t appears to follow that
organs already differentiated would in
no case become united to hCmUl0gOus
ones. BY whatever means, however, the
abnormal fusion OF like parts is affected,
such examples throw light on the fire.
Quent presence OF organs which are
double during the embryonic period (and
| so remain throughout lite in lower mem.
bcrs of the same class, but which after
ward unite into single orGan.
1t would seem that multiple and no
molegous organs are especially Liable TO
vary in number, and probably in torn.
As the supply of organized matter is not
unlimited, the principle Of " comprnSa
ton" sometimes comes into action, so
that when one part is greatly developed
adjoining parts are likely to be reduced {;
but this principle is believed to be OF
much less importance than the more gen
eral one of economy OF growth. Again,
through mere mechanical pressure bard
parts occasi onaly affects parts adjacent
With plants, moreover, the position oi
| flowers ON the axis sometimes leads
through a more or less flow Or sap to
changes of structure, Notifications, in
whatever manner caused, will he to II
certain extent controlled by that ca ordi
mating power, formerly styled the His"s'
t6rmatirus, which is III fact, n remnant ef
that simpl' ioIm Of reproduction dis
played by many lowly organized beings
in their power Of fssiparous generation
and budding. Finally, the effects OF
the laws which directly or indirectly gov
crn Variability may be largely regulated
by mans selection, and may be presumed
10 be 10 far determined by natural sclcC.
tions likewise, that changes beneficial to
any race Will be favored, and disadvan'
,ageous changes checked.
1t is obvious that all these laws of VI.
ration, rs well ms the several modes OF re-
production, stand in some sort of relation
to one another, and Darwin finds himself
impelled to postulate a principle which
to certain extent unifes and interprcts
them. Every one would wish" he says,
"to explain TO himself even in IN imper-
feet manner how it is possible for char
actcr possessed by some remote ancestor
suddenly 10 reappear in the offspring;
how the effects OF increased or decreased
use Of limb can be transmitted To q
child; how the male sexual element can
act not solely on the ovnles hut OCCASION
ully on the mother form" influencing the
offspring by subsequent fatherE show
a hybrid can be produced by the union
of the cellular tissue of two plants indie.
pendently of the organs of generation, las
in some cases ofgraftingE how limb can
be reproduced on the exact line Of am.
puta,ion with neither too much nor too
little added; how tho vesy same organ.
ism may he produced by such widely diff
terent processes Us budding and true
seminal generation, and hssly, how Of
two allied fnrms one passes in the course
Of its development through the most COM
plex metamoTphoses and the other does
not do so, though both when mature are
alike in every detail Of structure"
To elucidate these diverse facts, Oar
win proposes his hypothesis Of pangen-
esis, which implies That every separate
part of the whole organization repro
duces itself In other words, ovulcs,
spermatozoa and pollen grains, the fcrtil-
lied egg or seed as well as bud, include
and consist vt multitude of germs
thrown OFT from each separate cell cr
unit. This theory embraces such vast
applications and is so strenuously sup.
ported by its author that it deserves some
what careful analysis.
Reproduction may be divided into two
main classes, namely, sexual and non
sexual. The latter is effected in many
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