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PROTOZOOLOGY 



sumably certain substances are secreted by the organisms and be- 

 come diffused in the culture fluid. In the case of P. aurelia, Sonne- 

 born considers that there are also some substances which however do 

 not diffuse into the surrounding medium, and possibly transported 

 from one individual to another by contact and subsequent migration. 

 Fuller understanding of the phenomenon of mating types depends 

 upon future investigations. 



When the ciliate possesses more than one micronucleus, the 

 first division ordinarily occurs in all and the second may or may 

 not take place in all, varying apparently even among individuals 

 of the same species. According to Woodruff, in Paramecium aurelia, 

 of the eight micronuclei formed by two fissions of the two original 

 micjonuclei, only one undergoes the third division to produce 

 two pronuclei. This is the case with the majority, although more 



Table 6. — Varieties and mating types in Paramecium aurelia, P. bursaria and 

 Ewplotes patella. 



+ indicates that conjugation occurs; — indicates that it does not. 

 Paramecium aurelia (Sonneborn) 



