756 CALKINS. [Vol. XV. 



appears to be equivalent to the archoplasm of Boveri and the 

 centrodesmus of Heidenhain. In the more primitive forms, 

 unfortunately, the behavior of the intra-nuclear " achromatin " 

 during division is not well enough known to warrant definite 

 conclusions, although the fragmentary evidence which has been 

 gathered from various sources is sufficient to show, I believe, 

 that structures possessing all of the attributes of archoplasm 

 are present in the various forms. Its history is well known, 

 indeed, in Eiiglena, but here we are confronted with the assump- 

 tion, by Keuten and others, that the intra-nuclear element is a 

 centrosome or its equivalent. There is reason to believe, how- 

 ever, that the two poles of this achromatic body represent the 

 pole-plates of other Protozoa, and that the connecting rod repre- 

 sents the central-spindle. If this hypothesis is correct, the 

 achromatic body in the nucleus of Eiiglctia must be considered 

 equivalent to the sphere in Noctiliica and to the archoplasm of 

 Boveri or the centrodesmus of Heidenhain. 



With our present knowledge it is impossible to go farther 

 back than Ejighna for the development of archoplasm, and the 

 conclusion which may finally be drawn from our present knowl- 

 edge of this difficult question seems to be that primarily there 

 was a specific substance of the cell (archoplasm in Boveri's 

 sense) connected in some way with the mechanism of cell divi- 

 sion, and forming a definite intra-nuclear body {Englena). 

 Secondly, that this body became permanently e.xtra-nuclear, but 

 still connected with nuclear division {Noctiliica, and Metazoa 

 with "centrodesmus"), and finally that it became lost in the 

 cell and indistinguishable from the cytoplasmic reticulum (cells 

 without archoplasm or centrodesmus, most egg cells). 



The close similarity of mitosis in Noctiliica and Metazoa 

 does not necessarily indicate any phylogenetic connection. Nor 

 do the various Protozoa, which in this analysis are necessarily 

 brought together, show phylogenetic characters. We are at 

 present unable to develop any phylogenetic theory from the 

 facts of nuclear division. All that can be maintained is that 

 mitosis, in its many complicated phases, may have passed 

 through stages of development which are to-day represented 

 by many different and unallied types of Protozoa. 



