PROTOZOAN GERM PLASM 



575 



surrounded by a thickened zone of protoplasm and then each divides 

 twice, thus increasing the number of the zones. All of the protoplasm 

 is utilized in this zone forrriation, with the exception of a small portion 

 surrounding the original " primary " nucleus, these parts degenerating 

 and disappearing. Preparations of the decalcified individual at this 

 period show hundreds of minute nucleated masses completely filling the 

 shell space (Fig. 6). In life, these emerge in swarms, each in the form 

 of a tiny bi-flagellated swarmer. The swarmers are gametes which 





D 



Fig. 8. 



After Calkins. 



conjugate with similar gametes from another individual (Fig. 8, A). 

 The flagella are thrown off after union, the nuclei unite, and each united 

 pair, as a fertilized cell, or zygote, develops into a new micro sphseric 

 individual. 



In PolystomcUa, therefore, fertilization is accomplished, not by 

 union of the parent individuals as in Paramecium, but by coalescence 

 and fusion of minute gametes which contain portions of the specific 

 germ substance in the form of chromidia. 



