Relation between Nucleolus and Chromosomes. 59 
some cases. The female pronucleus is formed from the fusion of five or six 
vesicles, the product of transformation of the eighteen chromosomes remain- 
ing in the egg after maturation. 
At no stage in the maturation process are all of the chromosomes at the 
same stage of transformation. Almost every spindle shows several chromo- 
somes lagging far behind (figs. 64, 67, 68, 73). This explains why the 
counting of the chromosomes in polar view becomes difficult, not to mention 
their minute size. The most favorable sections for counts are such as pass 
longitudinally through the poles of a prophase figure. Since the chromo- 
somes are scattered through the equatorial plane, sections of from 7 to Io 
microns often include the major part of all the chromosomes. Such sec- 
tions almost invariably show 18 chromosomes in prophase (fig. 64). Simi- 
lar sections through the anaphase stages again invariably show 18 chromo- 
somes. The number could never be made less than 18; frequently in 
the anaphase of the first division 20 (occasionally even 24) V-shaped and 
bilobed chromosomes were counted, but these counts could usually be satis- 
factorily reduced to the usual number by taking into account the fact that 
some had prematurely split in preparation for the second mitosis. Polar 
views of either the prophase or anaphase stage also never showed less than 
18 chromosomes. This exact number could frequently be counted (figs. 76, 
77, 80), but in such sections even more frequently than in longitudinal 
sections of the spindle the number counted was 20 (fig. 79), 22, 23 (fig. 
78), or even as high as 24 chromosomes. It is very evident that prema- 
ture splittings of bivalent or univalent chromosomes—the normal process in 
the first maturation division—would raise the count in such sections and 
show wide and illusive variations in number. The best evidence shows that 
the reduced number of chromosomes is 18. 
THE REDUCTION OF THE CHROMOSOMES. 
The maturation phenomena of Asterias forbesii agree with those re- 
ported by Bryce in Echinus and likewise present a simple case of double longi- 
tudinal division. My results are at variance with those reported by Tennent 
(1905) for this same species. Tennent describes the second maturation divi- 
sion as transverse, separating bilobed chromosomes into chromosomes of glob- 
ular shape. I have conclusive evidence (figs. 73, 74) that the chromosomes 
resulting from the second polar mitosis are also for some time after their 
separation bilobed (dumb-bell-shaped) bodies and only subsequently become 
stubby or globular. The fact that the eggs observed by Tennent had under- 
gone previous treatment with CO, in sea-water, which seems to have greatly 
retarded the maturation process (40 minutes according to Tennent), may 
account for the discrepancy in appearance of the chromosomes. It is pos- 
sible that in the CO, treated eggs the bilobed chromosomes had become 
globular proportionately earlier—in consequence of a much slower transit 
toward the spindle poles—than in eggs under normal conditions. 
