THE COLONIAL HABIT IN SOME LOWER ORGANISMS 11
Somewhat similar double individuals have been recorded among
the Chrysophyceae, as for example, Didymochrysis which has
paired chromatophores, eyespots, and two pairs of flagella, and
here there seems reason to believe that such forms have arisen
as a result of arrested division, after which the partially divided
organism assumed a vegetative existence.
Again we have the peculiar organisation seen in one or two
flagellate Dinophyceae. The marine Polykrikos is probably
the best known; here two to eight cells form a chain ; each
cell has the characteristic transverse and longitudinal furrows,
the latter united to form a common groove ; but reduction may
occur in the number of nuclei so that a four-celled chain may
have but two, an eight-celled chain four or even two. Similar
cell chains are seen in other Peridineae ; thus in Gonyaulax the
protoplasts of the chain of cells are continuous, although there
is probably no reduction in the number of nuclei, as in
Polykrikos.
The idea that the colonial habit might lead, through the
coenobium, to the multicellular habit seems to be untenable
and it would seem that we must look elsewhere for the origin of
cellular organisms. Possibly with advancing knowledge we
may find the answer in organisms of the "double individual"
type, or perhaps the coenocytic type of organisation will furnish
us with clues. As for the colonial habit, as far as it concerns
the Protista, there is, in the present state of our knowledge, but
one answer to the question, where has it led, and that is, nowhere.
LITERATURE
(No attempt has been made in this article to give references to literature ;
those who may wish to supplement the information which it contains will
find useful the following selection of works, which are all copiously illustrated.)
Butschli, O. 1883-7. Mastigophora in Bronn Klassen und Ordnungen
des Tierreiclis 1, Abt. 11, Leipzig.
Fritsch, F. E. 1935. Structure and Reproduction of the Algae, J. Cambridge.
Kent. W. S. 1880-2. Manual of the Infusoria. London.
Kudo, R. R. 1939. Handbook of Protozoology. London.
Lemmermann, E. 1910. Kryptogamenflora der Mark Brandenburg 3.
Algen, 1. Leipzig.
Smith, G. M. 1933. Freshwater Algae of the United States. New York.
------------. 1938. Cryptogamic Botany, Vol. 1. New York.
Stein, F. 1878. Der Organismus der Infusionsthiere, III, 1. Leipzig.
Plate 2 (opposite). Colonial Protista (after various authors). A., Cla-
domonas fruticulosa Stein. B., B1., Chrysodendron ramosum Pascher; in
B1 a cell is dividing. C., Dendromonas Virgaria (Weisse) Stein. D., D1,
Dinobryon ; D, colony of D. divergens Imhof : D1, D. Sertularia Ehrenb.
one of the daughter cells of a recent division is seated at the mouth of the
parent lorica. E., Cyclonexis erinus Jane. F., Protospongia Haeckelii
Kent. G., Chrysarachnion insidians Pascher. H., Raciborskiella uro-
glcnoides Swirenko. J., Chlamydobotrys stellata Korsch. K., Rhizochrysis
Scherffelii Pascher. L., Hexamitus inflatus Duj. M., Didymochrysis
paradoxa Pascher.