STRUCTURE AND DIVISION OF ORGANIC CELL. 813 



can understand their disappearance, for the fibrils lose their net-like 

 reticulation, and become an irregular convolution, with no free ends. 

 Around this fibrous nuclear mass appears a clear space, which separates 

 it from the outer cell-substance. As thus arranged it forms what has 

 been called the aster. 



Soon the fibrous convolutions assume a wreath-like arrangement, 

 with their bends irregularly directed toward a central space. Eventu- 

 ally the wreath loses its continuity, and breaks into a series of short, 

 separate fibers, which form V-shaped loops. The bends of these loops 

 are directed toward the center space, their openings outwardly. This 

 arrangement forms the mother-star. Next there is shown a doubtful 

 appearance, as if the fibers had split into two, or had become tubular. 

 The loops are also compressed toward the equatorial plane of the nu- 

 cleus, and lose their extension toward its polar region. After some 

 further dubious movements, a rearrangement of the loops is found to 

 have taken place, their bends being now turned outward, their open- 

 ings inward toward the equatorial plane. They have also separated 

 in this plane, so as to form two distinct masses, one on each side of 

 the equator. If we consider the cell as a globe, and the equatorial 

 plane as a circular disk dividing this globe into two hemispheres, then 

 on each side of this disk lies a smaller circle of fibrous loops, which 

 present something of the aspect of a circular basket, or of a partly- 

 opened daisy. The openings of these basket-like figures are turned 

 toward each other, with the equatorial plane separating them. The 

 converging looped ends of the fibers are turned outward. 



This stage in the process of division of the nucleus is followed by 

 a recession of the basket-figures. They retreat in the axial line of the 

 cell until they reach the polar regions of the nucleus. Here a rear- 

 rangement of the fibrous loops takes place, their bends again become 

 directed toward a central space, and two new stars, similar to the 

 mother-star, are formed. The division of the chromatin, or fibrous 

 substance of the nucleus, has become complete, and the whole new 

 arrangement is known as the dyaster. 



As the basket-like figures recede, there often appear in the interval 

 between them delicate striae, which cross the equator from pole to pole. 

 This condition, which is most declared in vegetable cells and in seg- 

 menting ova, is known as the nuclear spindle. The lines of the strise 

 seem to be composed of achromatin. Other faint lines often radiate 

 from the poles toward the surface of the cell, forming sun-like figures 

 at the extremities of the nuclear spindle. Complete division is pre- 

 ceded by the appearance of a row of dots across the equatorial plane, 

 which seem to be thickenings in the centers of the lines of the spin- 

 dle. These thickenings are probably composed of chromatin, and 

 form what is called the equatorial plate. They soon divide, the spin- 

 dle separating in its center, while the thickenings appear like minute 

 disks at the extremities of the nuclear sti'iae. Thus a double equa- 



