1901.] NATURAL SCIENCES OF PHILADELPHIA. 265 



more or less uneven contours; and attached to it is a smaller true 

 nucleolus (X. ) which disappears in the following prophase by gradual 

 decrease in volume. Somelimcs there are two cliromatin nucleoH, 

 generally of different volumes; since in such cases neither of these 

 has the volume of the single one, they probably represent separated 

 parts of the latter. 



In the prophases of the first maturation mitosis, which follow 

 immediately upon the stage just described, the chromatin nucleolus 

 shows itself to be composed of four dumbbell-shaped (hence bival- 

 ent) parts of unequal volumes, arranged close together (N. 2, fig. 

 13), Necessarily all four parts must have been present in the 

 preceding stage, but have been optically inseparable ; the apparently 

 single chromatin nucleolus of the growth period is made up in 

 reality of four bivalent ones. There is great divei'sity in the mode 

 of mutual apposition of the latter in the prophases; sometimes the 

 long axes of all may be parallel, but more frequently they cross 

 one another at varying angles; no case was seen where all four lie 

 in the same plane. Quite frequently there are only three chroma- 

 tin nucleoli in mutual contact near the centre of the nucleus, while 

 the fourth is separated from them and placed against the nuclear 

 membrane (fig. 12). All four are true chromatin nucleoli, main- 

 taining throughout the growth period their dense structure, even 

 contours, and red stain with the saffranine-violet method of Her- 

 mann, while the chromatin of the chromosomes proper stain 

 ■violet. In the prophase we are considering are found also six 

 bivalent chromosomes (portions of all of Avhich are seen in fig. 13) ; 

 these are tetrads with very wide longitudinal splitting of the type 

 characteristic for Aiiasa (Coreid), Toward the close of the 

 prophase these chromosomes shorten and become much more com- 

 pact structures. 



Pole views of the monaster stage of the first maturation mitosis 

 (fig. 14) show in every case ten chromatin elements of compara- 

 tively large size. Four of these must correspond to the four 

 chromatin nucleoli, and six to the six chromosomes proper of the 

 preceding stages, since there has been no loss nor multiplication 

 of any of these elements. Of the ten elements of the stage of 

 fig. 14, one (j).) oa pole view always appears round, on lateral 

 view (p., fig. 16) it shows a simple dumbbell shape; this one, 

 much smaller than any of the others, probably represents one of 



