PROTOZOA 



193 



division, but the individuals may frequently be seen to 

 conjugate, whereby a certain amount of their proto- 

 plasmic substance is interchanged. This differs from 



y -'iW/ Wfl T^.7 S -"^S^T?'" "/^>%fe> n 



^^^ Drawing by W. P. Hay 



FIG. 42. Paramecium. .4, anterior; B, posterior end; m, oral opening; cv 1 , an- 

 terior contractile vacuole in contraction ; cv 2 , posterior contractile vacuole in state 

 of expansion; /, food masses ; w 1 , micronucleus ; w 2 , macronucleus. Greatly mag- 

 nified. 



the sexual reproduction of the Sporozoa, and it can 

 hardly be said that sex exists, since the conjugating 

 individuals are alike. In the Suctoria cilia are nearly 

 always absent in the adult, which possesses tentacles 

 instead. 



Cilia are by no means confined to the Protozoa ; thus 

 they exist in the human windpipe, where they serve to 

 remove the accumulations of mucus and dust. 



