760 CALKINS. [Vol. XV. 



higher forms, its attractive force keeps the granules together 

 during resting phases as well as during division (Cliilovwnas, 

 Trachelomonas, etc.); and, finally, that in still higher forms a 

 nuclear membrane is formed about the whole {Eiiglcna, Tracli- 

 elomonads, Syniira, ciliates, etc.). But another line of develop- 

 ment may have arisen from this primitive type. In some forms 

 the archoplasm may have remained outside of the aggregate of 

 chromatin granules, becoming secondarily centralized in the 

 manner described by Schaudinn ('96) for the division of the 

 flagellate-stage of Paramoeba, or in the same way as the central- 

 spindle in Noctiliica becomes centralized. In this way the 

 sphere in metazoan cells may have arisen without any connec- 

 tion with the intra-nuclear body of most Protozoa, while the 

 centrosome, as Flemming ('97) suggests, is an organ of second- 

 ary importance in the cell and which may or may not be 

 present.^ 



May 24, 1898. 



1 G. N. Calkins, The Phylogenetic Significance of Certain Protozoan Nuclei. 

 Ann. N. Y. Acad. Sci., vol. xi, no. i6, 1898. 



