CONJUGATION OF PAUAMCECIUM. 171 



readied, and the degenerative tendency seems to be checked by 

 a process known as conjugation. In this process two individuals 

 place themselves side by side, partially fuse together, and remain 

 thus united for several hours (Figs. 88, B, C}. During this 

 Union an exchange of nuclear material is effected, after which 

 the animals separate, both macronucleus and micronucleus now 



Fio. 88. A. Fission of Paramcecium. (From a preparation by G. N. Calkins), mac, 



macronucleus ; mfc, micronucleus ; rn, mouth. 



S. First stage of conjugation. The animals are applied by their ventral sur- 

 faces; the only change thus far is the enlargement of the micronuclei. 

 C. Conjugation at the moment of exchange of the micronuclei (less magnified). 

 The macronuclei are degenerating. Each individual contains two micronuclei 

 (now spindle-shaped), one of which remains in the body, while the other crosses 

 over to fuse with the fixed micronucleus of the other individual (After Maupas.) 



consisting of mixed material derived equally from both individ- 

 uals. Separation of the two animals is quickly followed by 

 fission in each. 



In each individual the macronucleus breaks up and disappears. The 

 micronucleus of each divides twice, and of the four bodies thus produced 

 three disappear. The fourth divides again into two, one of which remains 

 in the body, while the other crosses over and fuses with one of the micro 

 nuclei of the other individual, after which the animals separate. This 

 process being reciprocal, each individual now contains a micronucleus con- 



