62 THE AMERICAN NATURALIST [Vol.XLVI 



maturation and fertilization, that shows a most striking 

 parallel to that of the factors of determination. That a 

 somewhat similar apparatus of distribution may exist 

 also in the protoplasm of the cell is indicated both by 

 recent observations on the chondriosomes, or plasto- 

 somes, and by earlier results on experimental embry- 

 ology. If in the brief discussion that follows I confine 

 myself to certain phenomena of the nucleus it is because 

 the history of the chromatin is more fully and accurately 

 known. 



The progress of cytological inquiry tends steadily, I 

 think, to sustain the view first clearly formulated by Wil- 

 helm Roux that the nucleus contains many different sub- 

 stances which undergo orderly groupings and distribu- 

 tions in the karyokinetic phenomena. These processes 

 are in some measure made visible to us in the formation 

 of spireme-threads, in their history in cell-division, and 

 in the still imperfectly understood but perfectly definite 

 events of synapsis and reduction. In his well-known 

 paper on the significance of the karyokinetic figure, pub- 

 lished in 1883, Eoux maintained that the nucleus is the 

 seat of many different "qualities." He committed him- 

 self to no definite view as to what these "qualities" 

 really are; but the implication is not far to seek that they 

 have a chemico-physical basis and may be different chem- 

 ical substances. On this general assumption he based his 

 well-known interpretation of karyokinesis, of which the 

 essential postulate was that the ' 1 qualities ' ' ( substances ?) 

 become arranged in linear series in the spireme-thread, 

 and by longitudinal splitting of the thread may thus be 

 equally divided (or otherwise definitely distributed) to 

 the daughter-nuclei. I believe that many of the later 

 advances of cytology lend additional support to this con- 

 ception. 



1. In the first place, the evidence gives strong ground 

 for the conclusion that the chromosomes, to which the 

 spireme-thread gives rise, are not homogeneous, but com- 

 pound bodies. I do not here refer to the well-known fact 



