222 MURIEL ROBERTSON. 
elass-shaped ; finally it shps out, keeping the hour-glass shape 
until almost quite free. While in the free swimming state the 
creature is capable of becoming amceboid and of again recover- 
ing its original shape without withdrawing the flagella. 
Well-fed flagellate individuals can be seen to divide in the 
free state by transverse fission, but I have never seen this 
occur twice in succession in a specimen out of the colony, nor 
have I ever been able to observe it in creatures which had 
been without food for some time. Cold, or prolonged lack of 
food, causes the animal to withdraw its flagella, round itself 
off, and sink to the bottom of the pond, but I have never 
observed the formation of a very definite cyst.} 
The flagellate Pseudospora soon attacks another colony, but 
not as a general rule so long as it contains green food particles. 
if water containing free-swimming individuals is put into a 
tube with healthy Volvox the first to attack are those which 
still contain brown particles. ‘Those specimens, curiously 
enough, which are quite transparent owing to the absence 
of food particles, take from twelve to twenty-four hours, or 
sometimes even longer, before attacking the Volvox colonies. 
Pseudospora are often seen to attack both Hudorina and 
Pandorina even when Volvox are present, and on some occa- 
sions when starved they ingested small green alge, but I have 
never seen Spirogyra or other filamentous alge attacked. A 
starved Pseudospora sometimes ingests another Pseudospora 
which is densely filled with green food particles. This appears 
to be merely a process of feeding and to have no connection 
with either conjugation or association. 
I have never observed the formation of a true plasmodium, 
but temporary fusion of the protoplasm only may occur be- 
1] have been unable to find the double-walled cyst described by Cienkowski. 
The rounded-off Pseudospora appears to possess a more definite covering than 
the flagellate or ameeboid individuals, but nothing that in my opinion would 
justify the term cyst. 
These rounded-off individuals disintegrate at once upon the drying up of the 
water, so far as my experience goes. This may, however, be due to the 
process having taken place too rapidly. 
