462 MR. H. SANDON ON PKOTOZOA FROM THE 
between tlie flagellum and the surface to which it is applied, may however 
occur in other organisms having what has so far been regarded as a passive 
trailing flagellum. It is impossible, for instance, to watch a Cercomonas for 
long without concluding that its characteristic gliding motion is not produced 
by the tractellar action of the anterior flagellum, for the motion continues 
without a break even when this flagellum is temporarily motionless or 
recovering from its stroke ; and, further, the mean position of the flagellum 
often forms a wide angle with the direction of motion of the organism, which, 
on the other hand, is always in a line with the posterior flagellum. The 
movements of Cerecomonas and Helkesimastix are in fact so similar (in a 
casual examination it is easy to mistake Helkesimastix for a small Cerco- 
monas) that it seems probable that they are both produced in the same 
way and that the motive power in both, as in Allantion tacliyj^loon, is really 
the so-called trailing flagellum. 
When Allantion is not moving in this way, it adheres by the tip of the 
flagellum to the slide and jerks violently from side to side without progressing 
as a result of repeated flexions and extensions of the flagellum. 
Remains of ingested bacteria are sometimes found, so that nutrition is 
apparently holozoic though the actual method of feeding has not been 
observed. No cysts of this species have been identified. 
Though this organism does not appear to have been described before, it 
occurs very commonly in soils both from Europe and from the tropics. 
Anisonema minus (n. sp.). (Pi. 24. fig. 13.) 
This species is quite typical of the genus in all except size. It is usuallj^ 
from 6 /x to 7/x in length and never exceeds 9/x, whereas the lowest limit for 
any Anisonema given by Senn (30) is 11 /i. It is strongly flattened and has 
a longitudinal groove on the under side. In outline it is egg-shaped, but 
slightly asymmetrical at the antei'ior end. The anterior flagellum is stout 
and about equal to the body-length, while the posterior flagellum is rather 
more slender and about twice as long. They arise from separate basal 
o-ranules a little way behind the anterior end. The contractile vacuole is 
central, but a pharynx has not been definitely discerned. There is a large 
elliptical vesicular nucleus lying to one side of the body, containing a karyo- 
some, which though usually spherical is sometimes irregular in shape, and 
a ring of peripheral chromatin. The movements are slow and very steady, 
being produced by the movements of the anterior flagellum, which lashes 
through a wide amplitude. 
This species occurred in one sample only. I have, however, found it in 
soils from the West Indies, so that although apparently never abundant, it 
seems to be a widely- distributed soil form. 
Cladomonas sp. — This occurred in only one culture from soil sample 5 
(1921) . The monads are spherical to ellipsoidal in shape, from 5 //.to 1 [j, in 
length, and with two forwardly-directed flagella, each about 1^ to If times the 
