SOILS AND MOSSES OF SPITSBERGEN. 463 
body-length, inserted at the anterior end. Each monad is situated at the end 
of a tube usually with only the flagella projecting, but sometimes the cell 
itself protrudes to some extent. The tube is colourless and transparent, and 
is quite empty except for the organism at its tip ; in fact, but for the cocci 
adhering to it, it would easily pass unnoticed. Its composition was not 
investigated, but it is flexible and yields to the movements of the organism. 
Occasionally one finds an unbranched piece of tube, 50 /* or more in length, 
with a single flagellate at its end, but more usually the tube branches, though 
not with the regular dichotomy of C.fruticosa Stein. Usually, however, the 
distal parts of the tube are surrounded with a dense mass of bacteria, pro- 
tozoal cysts, etc., so that its ramifications cannot be fully followed out. The 
flagella are held at an angle of about 20° to one another and vibrate rigidly 
without bending. These movements are so rapid that the flagella can then 
only be detected by the characteristic movements of the surrounding bacteria, 
etc., one or two of which usually adhere to the tip of each flagellum, and are 
seen to be whirling round in a small circle. Occasionally the motion stops, 
and the animal remains at rest for a few seconds. The effect of the whirling 
of the flagella is to drive small bacteria towards the mouth of the tube, where 
they adhere both to the walls of the tube itself and to the body of the animal, 
which is consequently always the centre of a small mass of the organisms. 
Occasionally a single monad is found adhering to the glass slide without any 
tube. In this condition the flagella vibrate just as usual, causing cocci to 
come against the body, to which they then adhere. 
This organism differs from C. fruticosa Stein onlj' in the less regular 
branching of the tube, a feature which hardly justifies the creation of a new 
specific name. 
Phalanstbrium soLiTARiuM (n. sp.). (PI. 24. figs. 14, 15 & text-figs. 1, 2.) 
This organism differs, in several respects from the two established 
species P. consociatum Fresenius and P. digitatum Stein. It usually appears 
in cultures in the form of free-swimming monads 10 /tt to 15 /u, in length 
(text-fig. 1) and more or less spherical in shape, though sometimes rather 
elongated, and often distorted by the presence of large vacuoles. At the 
anterior end is a single fiagellum, three or four times as long as the body, 
which is surrounded at its base by a narrow " collar," into which a cyto- 
pharynx opens. The flagellum is very characteristic, the proximal part 
(about one-fourth of the whole length) being stout and fairly rigid, while 
the distal pai-t tapers to a very fine and flexible whip. Unlike the flagellum 
of the Craspedomonads, which is always a pulsellum, this flagellum acts as a 
tractellum, so that the creature swims with its collar directed forwards. 
A reversal of this mode of swimming has never been observed. The mode 
of swimming enables the species to be easily recognised, since the whole 
organism vibrates rapidly as it were about a pivot situated near the hinder 
end of the body. Often a few cocci adhere to the rigid part of the flagellum. 
