SOILS AND MOSSES OF SPITSBERGEN. 461 
but even after four minutes there are usually still a considerable number 
that have not resumed their movements. 
The cysts (fig. 10) are thin-walled, spherical, and from 4yu, to 5 /a in 
diameter. 'I'he contents are granular, the granules usually being arranged 
in a ring. When stained, a nucleus with karyosome iind peripheral blocks 
much as in the active stages is visible. 
It has not been found outside Spitsbergen, where it occurred in two samples 
of moss, both from Klaas Billen Bay. 
Allantion tachyploon* (n. gen., n. sp.). (PI. 24. figs. 11, 12.) 
This organism, though it resembles Sainouron in having a single flagellum 
which arises just behind the anterior end and is directed backwards, has such 
a characteristic mode of progression that one feels constrained to create a 
new genus for it. In size it varies from 7 fi to 14 /z (usually 8 /m-IO/j,), and 
the width is about half the length. The .shape is very constant, being 
equally rounded at the two ends and usually slightly crescentic. It is 
enclosed in a firm pellicle, and no trace of pseudopodia can ever be 
found ; in fact, the only deviations from the typical shape are the 
occurrence of shortened, almost spherical individuals, or of organisms which 
have their concave side (z. e. the side from which the flagellum arises) com- 
pressed, appearing in consequence moi-e transparent than the rest of the 
organism when they are seen in side view, and causing the animals to 
become triangular in cross-section instead of circular, as is more normal. 
Both these forms are commonest in rather old cultures. There is a simple 
vesicular nucleus with some peripheral chromatin in the anterior half of the 
body, and one or more deeply-staining spherical masses, presumably meta- 
bolic products of some kind, are often found in various parts of the body 
behind the nucleus. There is no contractile vacuole. The flagellum is about 
half as long again as the body, and is very much stouter than in such flagel- 
lates as Sainouron or Heteromita. It is invariably directed backwards. 
When the animal is pi-ogressing, the flagellum is applied for its whole length 
to the substratum, while the bodj^ itself is turned upwards at a sharp angle. 
Neither the flagellum nor the body of the animal show s an}' trace of vibration 
or movement of any kind, and yet the animal glides rapidly forwards, covering 
a distance of two or three times its own length per second. The organism 
whose movements resemble this most nearly is Helhesimastix Woodcock & 
Lapage (36), from which the present species differs in being quite without 
an anterior flagellum (the presence of which in Helkeslmastix I have been able 
to confirm, but which plays no appreciable part in the animal's locomotion). 
It also differs in the absence of a contractile vacuolej and in the presence of 
a firm pellicle as a result of which the flagellum is quite free except at its 
point of insertion instead of adhering to the body as it does in Helhesimastix. 
This mode of pi-ogression, depending presumably on some surface action 
* aKKdvTiov, a little sausage ; Td)(rjn\oou, swiftly-sailing'. 
