150 



SYSTEMATIC ZOOLOGY. 



of motion and by their aid the animal swims through 

 the water, or ; if fixed, creates currents which bring food 

 to it. Like other Protozoa these forms multiply by 

 dividing into two or more individuals, this process in 

 some being preceded by conjugation, which from its im- 

 portance from a theoretical standpoint needs a few words. 

 Conjugation is the union of two individuals. In many 



FIG. 6. A flagellate Infusorian, 

 Chilimonas paramcecium (after 

 Biitschli). n, nucleus; oe, 

 oesophagus; v, contractile vac- 

 uole. 



FIG. 7. A ciliated Infusorian, Stylo- 

 nichia mytilus, in process of division 

 (after Stein), a, anus; cv, contractile 

 vacuole; m, mouth; ma, macronucleus ; 

 mi, micronucleus ; nm, new mouth. 



cases the conjugating individuals are equal in size and 

 the union is temporary, the essential feature being an 

 exchange of nuclear material. Here we have the lowest 

 expression of sexuality, but without differentiation of 

 sex. With others the conjugating individuals are un- 

 equal in size and the fusion is permanent, the resulting 



