PELOSPHAERA ROTANS LAUTERBORN 65
rate some of them, must be provided with flagella, though I
have been unable to see them and Lauterborn says the same
of his specimens. The size of the colonies seen by me varied
from fifteen to twenty-two μ (Lauterborn says fifteen to forty
μ) and the cells from five to eight μ.
From the foregoing description it
seems clear that P. rotans is essentially
bacterial in character. It is, I believe,
the only case of bacteria normally
forming free-swimming spherical col-
onies although very young stages of
the sulphur bacterium Lamprocystis
roseo-persicina may be nearly spherical
and sometimes motile and may there-
fore, in this respect, perhaps be classed
with P. rotans. 
 Pelosphaera rotans. Show-
So far as I am aware P rotans ing enlarged upper cells
has only been previously recorded by mostly containing a highly
Lauterborn (as already indicated) and refractile globule (? spore).
F. Koppe (1924). I have found it in
Epping Forest as follows:—Pond on Leyton Flats, Pond on
Warren Hill, Pond in Gilbert's Slade and in "The Basin,"
Wanstead.
In connection with P. rotans it may be interesting to refer
to some other forms of micro-organisms which form free-
swimming spherical or nearly spherical colonies. Our President
in his address last year (F. W. Jane, 1947) called our attention
to the general question of the colonial habit in some lower
organisms and to the wonderful variety of such associations.
Incidentally reference was made to several cases of free-swim-
ming spherical colonies of microscopic organisms (e.g. Synura,
Pundorina, Volvox). But the number of such forms is actually
very considerable, as will be seen from the following list which
I believe can be regarded as fairly complete.
BACTERIA.
Pelosphaera rotans (and ? young colonies of Lamprocystis roseo-
persicina).
ZOOFLAGELLATES.
Oicomonadaceae—Oicomonas socialis.
Craspedomonadaceae (Choanoflagellates)—Sphaeroeca Volvox, S.
pedicellata.
Monadaceae—Monas sociabilis (and ? detached heads of Antho-
physa vegetans).
PHYTOFLAGELLATES.
Chrysomonadinae—Chrysopherella longispina, Syncrypta Volvox,
Synura uvella, Uroglenopsis europaea, U., americana, Uroglena
Volvox, Synochromonas spp., Skadovskiella sphagnicola, Chryso-
botrys Spondylomorum.
B 1