LIFE-HISTORIES AND THEIR LESSONS, 173 

formulated by the great Darwinian law. They increase immensely 
by cell multiplication, which in one section of the conjugatee remain 
united in long embranched threads of remarkable beauty. But the 
form of desmid, known as Cosmarium botrytis, has been sufficiently 
worked out by De Bary to serve as an excellent type. The cell is 
symmetrically bisected by a deep constriction, as in Plate I., Fig. 
3 a, but soon the narrowest part of this constriction elongates, 
then widens laterally, as in 4. This new process rapidly widens, 
lengthens, and takes the required form, until, as ¢, d, e indicate, the 
one cell has become two, which are in all respects perfect, and, freed 
from each other, rapidly repeat again this process, 
This goes on for an indefinite length of time, but it cannot goon 
for ever. It exhausts the vital capacity of the plant; there must 
be regeneration, the beginning of the cycle afresh. To this end, 
two of these elegant cells, placed together, and stimulated by what 
we have no means at present of discovering, open their cell walls 
and pour out their contents, which meet, as seen in F ig. 4 a, and 
fuse wholly together, deserting the original coverings, which are 
left empty beside the mass, as in 4, ¢c. The mass now rapidly be- 
comes spherical, forms a triple cell wall, and pushes out spinous 
growths, seen in d. The wall of the spine sphere now opens and 
sets free small spheres of sacrode, as ine. The history of each of 
these is the growth from it of two new cosmaria. A gelatinous 
wall forms, as in f, and a constriction of the contained sarcode is 
soon visible, which increases, as ing. Then each constricted half 
again constricts, and becomes again a symmetrically divided cos- 
marium cell, as seen in 2, The mother Cell wall is then absorbed, 
and the new cells separate from one another, and are free. 
With competent powers, patience, and a continuous non-evapo- 
rating stage, supplied with Cosmarium botrytis in vigorous vitality, 
this may be confirmed by any careful and competent observer. 
But he who supposes it can be done when the cosmaria are mingled 
in a cell with decomposing vegetable forms from a hundred other 
sources, present in the cell, giving rise to the production of the 
Septic organisms on the one hand, and a variety of epiphytic forms 
of alge, with all their complex, and in many cases unknown 
modes of development on the other, is wholly and absolutely 
mistaken, But let the life-history of this form, by itself, be thus 
carefully followed, and it will be seen to be from a biological view 
as rigidly, according to law, as that which in physics is known to 
be the determining cause of a lightning flash or the production of 
oxide of iron, ; 
But we may advance one step further. The confervoid alge are 
quite well known to the students of the pond and stream, and the 
thallus of the vaucheria is not unfamiliar amongst them. Now, it 
1s well known that. this lowly plant multiplies in two ways, but the 
