6S 



PROTOZOA 



conjugation produce the microspheric young. The microspheric 

 forms early become multinucleate, and have also numerous 

 chromidia detached from the nuclei, which they ultimately replace. 

 These collect in the outer part of the shell and aggregate into new 

 nuclei, around which the cytoplasm concentrates, to separate 

 into as many amoeboid young " pseudopodiospores " as there are 

 nuclei. These escape from the shell or are liberated by its 



Fig. 16. 1, Orbulina universa. Highly magnified. 2, Globigerina bulloides. Highly- 

 magnified. (From Wyville Thomson, after d'Orbigny.) 



disintegration, and invest themselves with a shell to form the 

 initial large central chamber or megalosphere. 



In the ordinary life of the megalospheric form the greater 

 part of the chromatic matter is aggregated into a nucleus, some 

 still remaining diffused. At the end of growth the nucleus itself 

 disintegrates, and the chromidia concentrate into a number of 

 small vesicular nuclei, each of which appropriates to itself a 

 small surrounding zone of thick plasm and then divides by 

 mitosis twice ; and the 4-nucleate cells so formed are resolved 

 into as many 1 -nucleate, 2-flagellate swarmers, which conjugate 



