THE WONDERS OF LIFE 



various stages of individuality which we distinguished 

 above (chapter vii.), we may indicate the following stages 

 of hermaphrodism and gonochorism. 



Some groups of protists, especially the highly or- 

 ganized ciliated infusoria (ciliata), are distinguished by 

 having a separation of male and female plasm within the 

 unicellular organism. The ciliata propagate, as a rule, 

 in large numbers by repeated division (by indirect cell- 

 cleavage). But this monogony has its limits, and has to 

 be interrupted from time to time by amphigony, a 

 rejuvenation of the plasm, which is effected by the 

 conjugation of two different cells and the partial de- 

 struction of their nuclear matter. By conjugation is 

 meant the partial and momentary union of two different 

 unicellulars, while copulation is a total and permanent 

 coalescence. When two ciliated infusoria conjugate they 

 place themselves side by side, and connect for a time by 

 means of a bridge of plasm. A part of the nucleus of 

 each has already divided into two portions, one of which 

 functions as the female standing-nucleus (paulocaryon) 

 and the other as the male travelling-nucleus (plana- 

 caryon). The two mobile nuclei enter the plasm-bridge, 

 and move through it, pushing against each other, into 

 the body of the opposite cell ; they then coalesce with the 

 deeper lying standing-nucleus. When a fresh nucleus 

 has been thus formed (by amphimixis) in each of the 

 copulating cells, they again separate. The two re- 

 juvenated cells have once more acquired the power to 

 propagate for a long time by division. 



This peculiar hermaphroditic formation of the cells, 

 which distinguishes the ciliated infusoria and some other 

 protists, and which we now know in its smallest details 

 through the investigations of Richard Hertwig, Maupas, 

 and others, is especially interesting because it proves 

 that the chemical difference between the female gy no- 

 plasm and the male androplasm can be found within a 



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