24 BRITISH FRESHWATER RHIZOPODA. 



reached he found that the process Avas 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 shell was retracted again into the old one, whilst one 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-lamella? 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 socialis (after Archer). x 500. 



individuals are constantly being formed, in many, pro- 

 bably all, of the shelled Khizopoda, as the result 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. g. Micro- 

 gromia socialis, Haphidiopkrys viridis). 



A form of division called " budding " has been noted 

 in the Arcellse and some Difflugise. A plasma " biid " 



