218 MURIEL ROBERTSON. 
each end, the pseudopodia elsewhere being usually, but not 
invariably, withdrawn. 
Occasionally the radial Pseudospora in the colony assumes 
a semi-amceboid appearance, the pseudopodia being for the 
most part withdrawn. In this condition it could not be dis- 
tinguished from an individual in the amceboid phase, which 
possesses fine pseudopodia arranged in bunches, were it not 
that here the amceboid shape is very transitory, the creatures 
soon again becoming radial. 
The protoplasm of the radial form is on the whole more 
homogeneous and translucent than that of either the flagel- 
late or the amceboid form; the contractile vacuoles are very 
large and conspicuous; four, and even five, are to be seen in 
the creature at one time. Occasionally they arise very near 
the surface as in a heliozoon, causing a temporary protuber- 
ance, which disappears when the vacuole bursts. 
In the radial phase the food particles are often contained 
in large vacuoles. The nucleus corresponds with that already 
described, but is usually somewhat smaller in size; its aver- 
age diameter is ‘0034 mm. The radial form is more passive 
than either of the other two forms; in the free state it floats 
much as an Actinospherium does or creeps in the manner 
already described. It attacks and leaves the colony without 
losing the radial character. It ingests Volvox individuals 
either by engulfing them bodily, or by passing them down a 
broad pseudopodium, or by drawing them towards itself by 
two adjacent pseudopodia, The radial form merges into the 
flagellate and amoeboid forms, from which it differs merely in 
shape and method of moving. It is, however, so far as my 
experience goes, always the predominant form in a culture 
where the Volvox are not moving. If the culture continues 
to be fed on Volvox in this condition the flagellate forms dis- 
appear entirely. The radial Pseudospora divides by fission, 
often without withdrawing the pseudopodia.' 
1] observed at different times a number of Pseudospora individuals—usually 
but not always of the radial type—which presented a peculiar and very evenly 
granular appearance. Upon being watched for some time the Pseudospora 
