898 
from another body (7. e., cell-family). There 
are, aS is well known, exceptions to the 
above; unending reproduction may occur 
without conjugation, as among such plants 
as are propagated by slips or suckers, and 
self-fertilization also occurs, but the general 
rule is as I have stated. A multicellular 
plant or animal in the successive stages of 
its development is therefore the homologue, 
not of the remote ancestral unicellular 
organism, but of all those successive genera- 
tions of unicellular organisms which inter- 
vene between one act of conjugation and 
the next. 
Unlike the cell descendants of a conju- 
gated unicellular organism, the cell-descend- 
ants of a conjugated germ differ from it, 
and from one another, in that they undergo 
differentiation along certain definite lines 
(into nerve, muscle, bone, ete.), the germ 
cells being so specialized that the cell-com- 
munities which spring from them are very 
like the cell-community of which they were 
cell-members, for which reason a man, for 
instance, is like his parent. Moreover, the 
cell-descendants of the conjugated germ 
differ from the cell-descendants of the con- 
jugated unicellular organism in that they 
remain adherent, and in that, in different 
lines of descent, they multiply at different 
though definite rates. Did the cell-descend- 
ants of the germ all multiply at an equal 
rate, a solid spherical mass of cells would, of 
course, result; whereas, owing to differences 
in their rates of multiplication, the shape 
of multicellular plants and animals are ir- 
regular (7. e., not spherical). But, though 
these rates of multiplication in different 
lines of descent are pretty definite in every 
species of plant and animal, they differ 
widely in different species, whence arise 
differences in shape betwixt one species and 
another. An ox, for instance, differs in 
shape from a man because in it the cells in 
different lines of descent do not multiply 
at the same rate as in the man. 
SCIENCE. 
[N.S. Von. VI. No. 155. 
We cannot doubt that, when first multi- 
cellular organisms were evolved from uni- 
cellular, all the cells constituting the mass 
were morphologically and physiologically 
similar, and that, therefore, like the ances- 
tral unicellular organism, every cell was 
capable of performing all the functions of 
life—food-getting, locomotion, reproduction 
of the race, ete. Later, as a result of 
natural selection, differentiation appeared 
among the adherent cells of the community, 
some taking on one function and some an- 
other, till at length a high degree of dif- 
ferentiation resulted, and the reproduction 
of the race was delegated to the germ cells. 
As I have already indicated, among the 
unicellular organisms every cell is a germ 
cell, and as such is capable of continuing 
the race. Among low multicellular organ- 
isms this power persists in many cells, and 
the environment decides whether it shall 
be exercised or not; thus, if almost any 
fragment of a sponge be bedded out it will 
proliferate into a complete individual. It 
persists longer in plants than in animals; 
thus from a fragment of begonia leaf may 
arise an entire individual capable of con- 
tinuing the race; the cells are being turned 
from their original destiny by a change in 
the environment. But among the higher 
plants this power of reproducing the entire 
individual by means of cells other than 
germ cells, or what may normally pro- 
liferate into germ cells, is very exceptional. 
All that commonly persists is the power of 
reproducing from such fragments of the 
complete organism as contain cells, which 
might normally proliferate into germ cells, 
the parts wanting to render the fragment a 
complete organism. Thus a geranium slip 
(for instance) contains cells which nor- 
mally (7. e., when the branch remains part 
of the plant) proliferate into germ cells ; if 
this branch be bedded out as a slip it pro- 
duces the roots which are needed to con- 
vert it into a complete organism of its 
