1916] Sicezy: fdnetofiurlfus of Flngcllatrs 187 



"idioplasm." This has resulted in the separation of the chromatin of 

 the protozoan cell into so-called ' ' generative ' ' and " " vegetative ' ' chro- 

 matin, corresponding respectively to the terms used in the metazoan 

 cell by Weismann. 



The writer wishes to take this opportunity to acknowledge her 

 great indebtedness to Professor Charles Atwood Kofoid, at whose sug- 

 gestion the work was begun, for the kindly interest and helpful criti- 

 cisms which have meant so much for its progress. 



B. HISTORICAL 



The present binuclear theory of Hartmauu is the direct product 

 of the earlier theories concerning nuclear relations of the cell. One 

 of the first to attempt a formulation of these relations was Biitschli, 

 whose work on the diatoms (1891) opened up a fruitful field for 

 speculation. With his discovery of the centrosome of the diatom 

 Surirella he attempted to homologize it with the mjcronucleus of the 

 Ciliata. A further extension of this idea was made by Lauterborn 

 (1893), working on the same subject. In 1894 Heidenhain carried it 

 still farther, homologizing these two structures with the centrosome 

 of the metazoan cell, making that organelle a derivative of the micro- 

 nucleus of the Ciliata, and the metazoan nucleus a derivative of the 

 macronueleus. In thus tracing out the line of development, the con- 

 dition found in the Ciliata is taken by Heidenhain as the primitive 

 one from which other forms, having a more specialized centrosome, 

 have arisen, finally culminating in the production of the metazoan 

 cell. This is an inversion of what seems to be the natural order. The 

 Ciliata evidently stand at the end of a highly specialized line rather 

 than at the beginning of the whole protozoan and metazoan develop- 

 ment. 



The hypothesis advanced by R. Hertwig in 1892 was very similar 

 to that put forth by Butschli the preceding year regarding the origin 

 of the centrosome. He suggested that it might be derived from one of 

 the nuclei of a binucleated cell which had lost its chromatin but re- 

 tained the active kinetic element required in division. The other 

 nucleus retains its chromatin but loses its active kinetic element. 



Lauterborn, in another memoir (1896), gives as the starting-point 

 for the development of the centrosome, not the Ciliata, but Amoeba 

 binucleata, a cell containing two equal nuclei. According to him two 

 lines of development took place here, one producing the two diiferen- 



