460 MK. H. SANDON ON PEOTOZOA FKOM THE 
the basal granule, but its size and shape seem to depend on the general 
metabolism of the organism rather than on the phase of its life-cycle, for 
dividing specimens can be found in which two nuclei are present, each 
entirely surrounded by a ring of plastin, whereas in other cases the plastin 
divides to form two centrally-placed spherical masses. The changes which 
this mass undergoes have unfortunately up to the present obscured the 
division changes of the karyosome, the difficulty of observing which is ren- 
dered greater both by the extremely small size of the organism and by the 
fact that the kaiyosome itself varies considerably in size and at times appears 
to be entirely lost (fig. 3), as in the case of Herpetomonas (Leptomonas) 
jaculans as described by Berliner (7). 
In old cultures thin- walled spherical cysts rarely reaching as much as 3/i 
in diameter appear (fig. 6). The protoplasm is uniform and shows no charac- 
teristic features, but tends to be denser round the periphery of the cyst 
and vacuolated in the centre. Staining reveals a simple excentrically- 
situated nucleus, the mass of plastin apparently having been lost before 
encystment. 
This species is very widely distributed. It is common in the Rothamsted 
soilj and has also been found in samples of soil from Africa, the West Indies, 
Azores, etc. 
Sainouron oxu (n. sp.). (PI. 24. figs. 7-10.) 
This species resembles the foregoing very closely. It is, however, con- 
siderably larger, being from 10 fi or 12 /a in length in a young culture, but 
diminishing to 6 /a or 7 /x in old cultures. The anterior end, instead of being 
rounded, is generally drawn out into a curved beak, at the base of which the 
flagellum arises (fig. 7). This beak is occasionallj' bent or flattened (fig. 8), 
and the whole body is in fact more plastic than in S. mikroteron. A large 
vesicular nucleus lies in the anterior part of the body, and is generally sur- 
rounded by a complete peripheral ring of chromatin (fig. 8), but frequently 
the ring is broken and in its place one or more deeply-staining masses 
(recalling the plastin masses of S. mikroteron') lie against the posterior part 
of the nuclear membrane (fig. 7). The basal granule from which the flagellum 
arises is situated at the base of the beak when the latter is present, or slightly 
to one side of the anterior extremity when the beak is not present. Usually 
the granule lies too close against the nuclear membrane to be distinguishable 
(fig. 9), but at times there is a considerable space between them (figs. 7, 8). 
In spite of careful examinations of cultures of all ages, no contractile vacuole 
lias been found. Nutrition appears to be saprophytic as in S. mikroteron, 
which species S. oxu also resembles very closely in its movements. It shows, 
however, one interesting peculiarity in its behaviour in that when a drop of 
a culture is put on a slide and covered with a coverslip for examination, the 
organisms remain perfectly quiescent for some time. The first signs of 
activity usually appear about one minute after the preparation of the slide. 
