MONOCYSTIS 159 



nucleus, the other extremity being produced into a highly- 

 contractile tapering process, the lashing movements of which 

 propel the organism. Once it finds its way into a sperm- 

 mother cell, the sporozoite enters upon an indolent phase, 

 grows in size, stores up nutriment, and only emerges when 

 ready for sporulation, the final preparation for this process 

 consisting in the extension of a part of its nuclear substance, 

 as a so-called polar body. The act of conjugation consists in 

 the commingling of the nuclear material of two perfectly similar 

 zygotes. One cannot distinguish an active from a passive 

 form, a male from a female ; and, after the commingling has 

 taken place, each zygote recovers a half of the combination 

 nucleus, and gives rise to spores. We shall see that far more 

 complicated processes take place in other Protozoa. 



