216 MURIEL ROBERTSON. 
many large green and brown masses are to be seen in the 
endoplasm. ‘The green particles are the still undigested 
Volvox individuals, the brown, those which are in process of 
digestion. Definite food vacuoles do not seem, as a rule, 
to be formed in the amceboid Pseudospora, that is to say, the 
outline of the vacuole is so close to the food particle as to be 
indistinguishable. Sometimes the creatures are so densely 
filled with food particles as to appear quite green. 
Very bright spherical particles, which are, as a rule, to be 
seen in Pseudospora individuals, which have sojourned for 
some time in the Volvox colonies, appeared, upon treatment 
with osmic acid, to be globules of some fatty substance. Two 
or three contractile vacuoles are present ; these are, however, 
not very conspicuous in either the amceboid or the flagellate 
forms. 
Nucleus.—The resting nucleus (figs. 1 and 2) measures 
about ‘0046 mm. to ‘0057 mm. in diameter. It is a single, well- 
defined body lying in the centre of the creature. It is 
bounded by a fine membrane staining with chromatin stains. 
Inside the membrane lies a deeply-staining spherical body or 
karyosome surrounded by a very definite clear space. In 
preserved specimens the karysome stains with Romanowski’s 
stain, safranin, Ehrlich’s hematoxylin, Heidenhain’s iron 
heematoxylin, borax carmin, and picrocarmin. The chromatin 
lies diffused through the karyosome, which presents, in the 
resting state, an almost homogeneous appearance. The 
karyosome is produced into fine rays, which pass to the 
nuclear membrane, these stain somewhat less intensely than 
the karysome. 
B. Flagellate form. Size, ‘012 mm. to ‘03 mm. 
The flagellate Pseudospora is an oval, oblong or pear- 
shaped creature bearing two flagella at one end (fig. 3) ; 
these are usually equal in length, though in many cases one 
is shorter than the other. The flagella are comparatively 
thick and do not taper at the end; they are two or three 
