THE COLONIAL HABIT IN SOME LOWER ORGANISMS 9
vegetative cell, is produced in each organism and 128 sperma-
tozoids are formed in each antheridium.
Of genera of the Volvocales in which the coenobium is not
imbedded in mucilage, the little known Pascheriella has a four-
celled coenobium although at times it may consist of but two.
Chlamydobotrys possesses a mulberry shaped coenobium with
eight or 16 cells arranged in tiers of four. Spondylomorum, in
which the cells have four flagella in contrast with the biflagellate
ones of Chlamydobotrys, is essentially similar. In these three
genera association between the individual cells of the coenobium
appears to be slight ; it is recorded that individual cells of
Pascheriella may break away from the coenobium and I have
noted six-, four-, three- and two-celled Coenobia in the normally
eight-celled Chlamydobotrys stellata Korsch. as well as the
occurrence of solitary cells ; in my opinion such Coenobia are
formed by the break up of the eight-celled ones, not the pro-
duction by mother cells of Coenobia of fewer than eight cells.
Compared with the colony, as defined in this paper, the coenobium
shows several peculiarities :
1. It has a definite form, and the number of its cells normally
remains constant. The exceptions just noted in Pas-
cheriella and Chlamydobotrys appear to be in the nature
of abnormalities.
2. The coenobium arises endogenously within a mother cell
and is released as a complete structure; it is not, like a
colony, built up from a single cell by longitudinal divi-
sions—in fact, it would appear that the first divisions
are transverse. Moreover, flagellate colonies may not
start as a single cell but merely by an approximate halving
of a larger colony.
3. The cells of the coenobium are walled (with the possible
exception of those of the little known marine Oltmann-
siella).
It seems difficult to avoid the conclusion that the coenobium
is a definite structural unit, and as such ought to be considered
as an individual ; it is not, like the colony, an indefinite aggregate
of cells, which, on reaching certain proportions, divides roughly
into two, or even more parts. It arises, moreover, like a multi-
cellular organism, from a single cell. If we turn our attention
to the Chlorococcales we shall find Coenobia which appear to be
strictly comparable with those which have just been considered.
Such is the coenobium of Coelastrum. In some genera, like
Pediastrum and Hydrodictyon, the Coenobia (for such they are
always called) are formed differently ; the contents of a cell
divide up into zoospores, which, either in the cell or in a bladder-