CONJUGATION IN UNICELLULAR FORMS 



223 



many of the Infusoria union of the cell-bodies is only temporary, and 

 the conjugation consists of a mutual exchange and fusion of nuclei. 

 It is impossible within the limits of this work to attempt more than a 

 sketch of the process in a few forms. 



We may first consider the conjugation of Infusoria. Maupas's 

 beautiful observations have shown that in this group the life-history 



Second fission. 



First fission, after separation. 



Differentiation of micro- and 

 macronuclei. 



"^ Separation of the gametes. 



> Division of the cleavage-nu- 

 cleus. 



Cleavage-nucleus. 

 Exchange and fusion of the 

 germ-nuclei. 



Germ-nuclei. 



Formation of the polar bodies. 



Union of the gametes. 



Fig. 109. — Diagram showing the history of the micronuclei during the conjugation of Para- 

 miecium. [Modified from MaUPAS.] 



.Y and K represent the opposed macro- and micronuclei in the two respective gametes ; circles 

 represent degenerating nuclei ; black dots, persisting nuclei. 



of the species runs in cycles, a long period of multiplication by cell- 

 division being succeeded by an " epidemic of conjugation," which 

 inaugurates a new cycle, and is obviously comparable in its physio- 

 logical aspect with the period of sexual maturity in the Metazoa. If 

 conjugation does not occur, the race rapidly degenerates and dies out ; 

 and Maupas believes himself justified in the conclusion that conju- 



