8i6 THE POPULAR SCIENCE MONTHLY. 



more deeply. The density of the chromatin appeared to increase in- 

 wardly. 



From the outer cell-wall fibers pass inward to the nuclear mem- 

 brane, which they probably penetrate, and become continuous with the 

 fibers of the nucleus. These, in their turn, seem to connect with what 

 appears to be a membrane of the nucleolus. Inside the latter there is 

 no evidence of fibrous structure. 



In cell-division the first stage is the aggregation, on opposite sideu 

 of the nucleus, in a line with the long axis of the cell, of a quantity of 

 pale, slightly granular protoplasm. This is perhaps derived from the 

 peripheral layer, and travels inward along the fibers, since minute 

 thickenings, of similar appearance, show themselves upon these fibers. 

 The nucleolus swells out into two protuberances, in the same axial 

 line, joined by a bridge of denser matter. This change is, perhaps, 

 connected with the division of the nucleolo-nucleus, since subsequently 

 two of the latter are visible, while the nucleolus returns to its former 

 state. At the same time it is found to have considerably increased in 

 size. The next visible change occurs in the nucleus, whose contents 

 aggregate at the nuclear poles, push through the membrane, and com- 

 bine with the outer aggregation of protoplasm to form two dark 

 amoeboid lumps. From these polar masses fibers run inward and out- 

 ward, though the external fibers have become loose and flaccid. 



In the next stage the nuclear membrane disappears. The spindle 

 of fibers which runs inward to the nucleolus is bordered by two darker 

 strands, possibly the remnants of the membrane. This composes the 

 nuclear harrel. The nucleolus divides by a dumb-bell-shaped constric- 

 tion, similar to what appears in the division of amoebse. It resembles 

 what Flemming calls " direct division." The two halves of the divided 

 nucleolus — each containing one of the nucleolo-nuclei — now move out- 

 ward toward the poles, a new line of fibers forming between them as 

 they separate. These bodies almost seem to have a repulsive energy, 

 for the polar masses recede before them. The connecting lines also 

 spread outward centrally, so that the nuclear barrel becomes consider- 

 ably elongated and widened. It resembles a barrel with thick, narrow 

 ends and widely swelled-out middle. Eventually the nucleoli reach 

 the polar masses, into which they penetrate, while the substance of the 

 latter spreads inward so as to inclose them. The rudiments of new 

 nuclei are thus formed, between which extend rows of fine fibrillar 

 lines, much separated centrally. The " nuclear barrel," with the nu- 

 cleolus in its center, has thus been succeeded by the " nuclear spindle," 

 with no central mass. 



There now appears a row of dots, stretching across the equator of 

 the spindle. This quickly separates into a double row. At the same 

 time the lines of the spindle are sundered centrally, and the dots seem 

 to be minute disks at their extremities. In this manner a double 

 " equatorial plate " is formed, inclosing the circular equatorial plane of 



