12 ART. 4. N. YATSU : 



(PI. II., Figs. 15-18.) free from yolk-granules. At both ends of 

 the spindle are centrosomes, around each of which a "heller Hof" 

 is present. The zone gradually passes over into a darker zone 

 (cortical layer) and this again into the clear outer zone of the 

 centrosphere : throughout all these layers astral rays are distinctly 

 seen. It may be noted that the distal region of the mitotic figure 

 is slightly elevated above the surface contour of the egg, the 

 vacuolar layer at this point having been thrust aside (PI. II., 

 Fig. 15.). The axis of the spindle seems to stand in no definite 

 relation to the egg surface ; sometimes the axis is almost para- 

 tangential to the ovum (PL IL, Fig. 17.), while in other cases it 

 is perpendicular to the egg-surface (PL IL, Fig. 18.). All inter- 

 mediate angles have been observed. I at first thought it possible 

 that the angle changed with the stages of the polar mitosis, but 

 on looking over the preparations I found that such was not the 

 case It is hardly necessary to repeat here that the nucleolus had 

 disappeared before the mitosis took place. At the anaphases the 

 centrosphere and centrosomes become invisible. 



After the second polar body is cast off eight réfringent rod- 

 shaped chromosomes are found in a clear space, which probably 

 represents dense nuclear fluid (PL IL, Figs. 16, 19.). From this 

 number the chromosomes in somatic cells are conjectured to be 

 sixteen. 



The egg-nucleus acquires at the same spot a distinct nuclear 

 membrane. Chromatin is distributed as very fine granules which 

 come to occupy the nodes of the nuclear reticulum (PL IL, Fig. 

 20.). The path along which the egg-nucleus makes its way 

 toward the centre of the ovum is clearly made out by the funnel- 

 shaped intrusion of the vacuolar layer into the yolk part (PL 

 IL, Fig. 20). 



