II 



PHYLUM PROTOZOA 



57 



flagellum or a pair of flagella. In some cases the flagellulse have been 

 observed to copulate in pairs. The young may develop shells while 



J-'K;. : J ,l). Dimorphism and alternation of generations in Polystomella crispa. The arrows 

 indicate the direction of the life-cycle. A, young megaspheric individual ; B. full-grown 

 megaspheric individual, decalcified ; C, megaspheric individual in the act of spore- 

 formation, the protoplasm leaving the shell in the form of flagellulae ; D, flagellula more 

 highly magnified ; E, microspheric individual developed from a flagellula ; F, microspheric 

 individual in the act of producing amoeboid embryos. 1, nucleiis ; 2, chromidia. (From 

 Lang, after Schaudinn.) 



still within the shell of the parent or only after becoming free. In 

 the dimorphic Foraminifera there is evidence of the occurrence of an 



