496 



BIOLOGY OF THE PROTOZOA 



be distinguished from ordinary asexual, vegetative individuals. 

 The latter tyj)e is represented by the vast majority of Infusoria, 

 and, as Minchin maintained, there is very little justification for 

 calling them gametes at all; yet they come together for purposes of 



FIRST MATURATION DIVISION OF MICRONUCLEUS 



5EC0ND AND THIRD 

 DIVISION OF MICRONUCLEUS 



THREE 50MATIC DIVISIONS OF FERTILIZED NUCLEUS 



FERTILIZATION 



TWO CONSECUTIVE DIVISIONS 

 GIVING FOUR NORMAL CELLS 



Fig. 20G.— Paramecium caudatum. Diagram of the fertilization processes. 

 (After Calkins.) 



fertilization and to this extent at least, resemble gametes. In the 

 majority of Protozoa fertilization involves the permanent fusion of 

 cell bodies as well as of cell nuclei and the term copulation is applied 

 to such cases. In the Infusoria fertilization involves the permanent 

 fusion of nuclei only, while the cell bodies, with few exceptions, are 



