REPRODUCTION— MITOSIS. 
379 
It is accomplished by the elongation of the nucleus, which becomes 
dumb-bell shaped ; the neck becoming further constricted and 
eventually dividing, forming two cells, the whole process being very 
rapidly accomplished. 
Mitosis (furos, thread) or indirect segmentation is the prevalent 
mode of nuclear division and ensures a more perfect dividing of its 
chromatin elements ; the process is characterized by the enlargement 
of the nucleus and the appearance of beautiful spiral stars. It is always 
preceded by the resting condition, the chromatin or stainable part 
having then the aspect of a complexly coiled thread, which gradually 
becomes more distinct, and breaks up into a number of sections or 
loops, the nuclear membrane and nucleoli disappearing, and the 
centrosomes becoming apparent at opposite poles ; these constitute 
the foci of a characteristic arrangement of protoplasmic fibres forming 
the spindle figure, the chromatic loops become arranged around it 
at the equatorial plane and contribute to form the Monaster or 
Fig. 708. Fig. 709. Fig. 710. Fig. 711. Fig. 712. Fig. 713. 
Diagrammatic figures representing various stages in the Mitotic or indirect segmentation of the 
nucleus (modified after Waldeyer). 
Fig. 708. — Resting nucleus, showing the encircling nuclear membrane, nucleolus and chromatin 
network. 
Fig. 709. — Polar view of “ Loose Skein ” stage, with centrally and excentrically disposed loops. 
Fig. 710. — Monaster stage, as seen from pole. c. cytaster or polar star ; ch. cleft chromosomes, 
radially disposed. 
Fig. 711. — Monaster stage, viewed laterally, c. cytaster ; ch. cleft chromosomes radially arranged 
around s.^ spindle figure. 
Fig. 712. — Dyaster or Twin-star stage, viewed laterally, c. cytaster, ch. cleft chromosomes 
separated and travelling along the spindle figure towards the poles to form the daughter nuclei. 
Fig. 713. — Separated nuclei, hut cell protoplasm not yet divided. remains of spindle figure in 
hilus of chromatic figure ; h. hilus or pole ; d. line of impending separation of the protoplasm of 
the two cells. 
equatorial plate, the angles of the loops being towards the centre of 
the spindle figure and the limbs projecting peripherally; the loops 
afterwards split longitudinally, the divided halves separating and 
travelling along the spindle threads to opposite poles to form twin 
daughter stars and constituting the Dyaster stage. These processes 
are accompanied by a constriction of the cell, transversely to the axis 
of the spindle, which continues until it is divided into two separate 
cells, the spindle, centrosomes, etc., disappear, and the chromatin of 
the now separate nuclei each acquire a new nuclear membrane and 
assume the resting condition prior to a repetition of the process. 
