228 University of California Publications in Zoology [VOL. 19 



microkaryosome there can be little doubt and this seems to persist as 

 the terminal knobs to the skein segments. 



That all the chromatin entering into the formation of the chromo- 

 somes can not possibly be of the original microkaryosome is obvious. 

 Considering the average individuals, the average size of the micro- 

 karyosomes when separated from the macrokaryosomes may be esti- 

 mated at about 1.5 to 2/u, in diameter. The size of six of the chromo- 

 somes may relatively be estimated at 0.75 x 1.5/u. each, the small one 

 being only half as large (pi. 12, fig. 50). All other chromatin is out- 

 side the kinetic membrane and it does not seem probable that it could 

 go through as granules or mass units, since the area immediately 

 around the kinetic membrane is hyaline and in a state of solution, 

 while the area within becomes filled with a dense chromatin cloud, 

 and the only chromatin masses consist of the persisting and re- 

 organizing elements of the microkaryosome. It appears, therefore, 

 that there is a solvent action within the hyaline area around the 

 membrane and that chromatin from the granules in the peripheral 

 zone, possibly from the macrokaryosome, and probably from that 

 encrusted upon the nuclear membrane, is dissolved and passed through 

 the kinetic membrane by diffusion and enters into the composition 

 of the chromosomes. This demands a higher pressure from without, 

 which can easily be accounted for by the chromatin within the mem- 

 brane being condensed and precipitated upon the achromatic linin 

 fibers of the skein. When the kinetic membrane has expanded to the 

 limits of the nuclear membrane, this early phase of a segmented 

 spireme (pi. 12, fig. 49) finally organizes into a skein resembling a 

 more or less continuous ribbon, with chromatin granules embedded 

 upon it. This seems to be accomplished by a longitudinal separation 

 of the segments, the terminal knobs especially showing this division. 

 A final split involving the formation of sixteen chromatin masses 

 (pi. 12, fig. 49) may be found and may be regarded as the precocious 

 splitting of the definitive chromosomes. From these chromatin masses 

 which are already arranged in an equatorial belt the seven or eight 

 chromosomes of the equatorial plate are finally organized (pi. 12, fig. 

 50), probably re-fused by a telosynaptic process. 



The interpretation of a segmenting spireme seems necessary 

 because of the fact that its elements seem to be directly produced 

 by the early division and organization of the microkaryosome, this 

 being evident before the metabolic membrane has expanded to its 

 final proportions. This spireme frequently has the appearance of a 



