RAND: NERVOUS SYSTEM OF LUMBRICID^. 131 



matic masses would result in two objects like the one seen in Figure 31. 

 Figures 32 a and 32 b i-epresent two young sister cells with several of 

 the surrounding nuclei. They lay in two adjacent sections, and by means 

 of camera drawings their centres were found to be exactly superposable. 



The interpretation of Figure 31 is obvious. The heavily stained 

 compact mass, concave upon one side, otherwise spherical, is one of two 

 daughter chromatic masses resulting from the fusion of a group of 

 daughter chromosomes. On the concave side of the chromatin is an 

 area distinguished by a stain distinctly lighter than that of the chro- 

 matin, but yet sufficiently heavy to outline it sharply against the outer 

 clear space. On the mid-border of this lightly stained region is a dark 

 granule. This granule is the centrosome, and the lightly stained region 

 coi'responds to the polar region of the old spindle. The chromatic mass 

 and its accompanying polar structures lie in an irregular, indefinitely 

 outlined, clear space. This clear space is the region formerly limited by 

 the old cell membrane, which has completely disappeared. In the later 

 stages of mitosis represented in Figures 27-30 various stages in the 

 degeneration of the cell membrane of the mother-cell are to be seen. 

 The dark masses (Figure 31) lying in the clear space, on the apolar 

 side of the chromatic mass, may be remnants of the old spindle. 



In Figure 32 a is a similar condition of the chromatic mass with the 

 lightly stained polar region on its concave side. No distinct centro- 

 some was visible in this case. The surrounding clear space marks the 

 region formerly bounded by the daughter-cell membrane. In Figure 

 32 h a more advanced condition of the chromatin is seen. The volume 

 of the chromatic mass has increased, and this increase is attended by the 

 separation of the chromatin into a number of large granules, between 

 which the mass has a lighter appearance. The concavity on the polar 

 side of the chromatin is still marked. The lightly stained polar region 

 is sharply outlined. It has increased in volume and lost its conical 

 form. The centrosome no longer lies -at its border, but well in toward 

 the concavity of the chromatic mass. There are some faint lines ex- 

 tending from the centrosome to the periphery of the lightly stained 

 region. Chromatic mass and polar structui'e lie in a clear space. 



Figure 33 shows two pairs of sister cells, a and /3 are to be regarded 

 as the chromatic masses of one pair. The chromatic masses of the other 

 pair lie one over the other, y is the upper of the two masses, and the 

 outline of the lower is indicated by S. In a and /? the condition of the 

 chromatin is much as in Figure 32 b. a shows the concavity of the 

 chromatic mass, the lightly stained polar region, and the centrosome at 



VOL. XXXTII. — NO. 3 4 



