220 MURIEL ROBERTSON. 
daughter colonies ; they are often to be seen lying in groups 
closely resembling the destroyed daughter colonies. Some- 
times the Pseudospora attacks a segment as large as itself, 
slowly absorbing it or even creeping into its interior if it is 
very large (fig. 6). 
As a rule the Pseudospora begins to feed at once upon 
arriving in the colony. One individual which I observed 
ingested no less than fifteen Volvox cells in two and a half 
hours. Nevertheless, starved or very young specimens will 
often lie in a colony for some time (six to seven hours) 
before beginning to feed. 
When well established in the colony, Pseudospora divides 
about once in every twenty-four hours (at temperatures 
6°—16° C.). When about to divide the creature withdraws 
its pseudopodia and becomes spherical in shape, and the food 
particles become arranged in a band round the centre. A 
constriction then appears and the animal divides in two, the 
daughter individuals usually lying in close proximity for 
some time after they are quite separate. Finally the creatures 
put out pseudopodia and creep actively away. ‘The time 
elapsing between the withdrawing of the pseudopodiaand the 
division of the animal varied between three quarters of an 
hour and an hour and a half in the specimens which I 
observed. 
The first preparations for division of the nucleus (figs. 7-11) 
occur, just before the animal rounds itself off, in the breaking 
down of the nuclear membrane. The whole nucleus seems 
nevertheless to be still quite separate and clearly defined 
from the general cytoplasm. The chromatin at this stage 
begins to gather together into irregular masses, giving the 
karyosome a somewhat mottled appearance. ‘The whole 
nucleus now increases in size and the rays become indistinct. 
The achromatic part of the karyosome can still be distin- 
guished, while the chromatin seems to have segregated out 
from it, forming a number of small masses lying towards the 
equator of the nucleus. Careful examination of the nucleus 
at this stage (fig. 7) shows a roughly oval structure with 
