3
THE COLONIAL HABIT IN SOME LOWER ORGANISMS
BY FRANK W. JANE, PH.D., D.SC. F.LS.
(Being a Presidential Address delivered March 30th, 1946)
IN this address it is not my intention to discuss the colonial
habit in general, but to confine my attention to the colony
in the Protista and in particular, to flagellate forms of the
Protista. Since there appears to be no very precise definition
of a colony, it is defined, for the present purpose, as "an aggre-
gation of individuals, alike and complete in themselves but
not normally occurring separately." This definition is not
perfect, and it would be even less so were the scope of the subject
extended to embrace all so-called colonial organisms; for those
under present consideration the definition is probably as useful
a one as can be devised.
The colonial habit is widespread among the Protista and
here no more than a general survey will be attempted. Colonies
of flagellates and their near derivatives fall broadly into two
types:—a, those in which the daughter cells of successive divi-
sions separate completely, but remain associated within a com-
mon mucilage, i.e., the mucilage contains a number of isolated
cells; b, those where the products of division remain to a greater
or lesser extent contiguous; such colonies also may have a
common mucilaginous investment.
Of the former type the most primitive would appear to be
that which occurs in species of Chromulina (e.g. C. mucicola
Lauterborn and C. Pascheri Hofender), where numerous in-
dividuals are embedded in mucilage. In Spongomonas intestinum
(Cienk.) Kent many thousands of flagellate cells are held to-
gether within a vermiform mass of mucilage which may attain
a length of three centimetres and a breadth of 0.2 millimetres,
or again the colony may assume the form of a flat plate, as in the
much-figured Protospongia Haeckelii Kent.
In some flagellate forms, like Chlamydomonas, the cells may
at times lose their flagella and divide repeatedly, during which
process they develop much mucilage ; such palmelloid stages may
be large, and may contain thousands of cells, and it would seem
that they are strictly comparable with the type of colony which has
just been considered. In fact, an interesting intermediate stage
is seen in Chlamydomonas Kleinii Schmidle where the palmelloid
condition predominates although the cells remain flagellate and
may even move slightly within the enveloping mucilage.
In some algae the palmelloid condition is dominant and
motility is confined to the reproductive cells, a condition seen