2-4, BRITISH FRESHWATER RHIZOPODA. 
reached he found that the process was arrested. 
Separation of the new individual from the parent did 
not take place; and not infrequently, whilst two shells 
and two nuclei were produced, only a single animal 
resulted. The plasma which filled the newly-formed 
shell was retracted again into the old one, whilst one 
of the nuclei was thrown off, and perished. The 
purpose seems to have been accomplished of ridding 
the parent of its superfluous shell-lamelle and of a 
part of its nucleus; but what the precise significance 
of the act may have been otherwise, is not apparent. 
On the other hand it may be assumed that new 
Fig. 12.—Stages in the reproduction (division within the test) of 
Microgromia soctalis (after Archer). x 500. 
individuals are constantly being formed, in many, pro- 
bably all, of the shelled Rhizopoda, as theresult of perfect 
fission, one half of the divided nucleus always going to 
the daughter cell. 
In some testaceous species complete division takes 
place within the shell. The daughter individual, fur- 
nished with nucleus and contractile vacuole, migrates 
in the amoeboid state, secretes a shell for itself, and 
may either follow an independent existence or unite 
with the parent to form part of a colony (e.y. Miero- 
gromin socialis, Raphidiophrys viridis). 
A form of division called “budding” has been noted 
in the Aveclle and some Difflugie. A plasma “ bud” 
