190 



KAKYOKINESIS. 



contain only half the usual number of chromosomes, consequently the male pro- 

 nucleus, which is formed from the nucleus of the spermatoblast (head of the 

 spermatozoon), also is formed by one half the usual number. The same is the 

 case with the female pronucleus which has parted with one half its total number 

 of chromosomes in extruding the second directive corpuscle, so that the blending 

 of the male and female pronuclei restores to the ovum its full number of chro- 

 mosomes, and since in the division of this and in all subsequent processes of division, 

 the chromosomes split and pass half into the one and half into the other daughter- 

 nucleus, the number of chromosomes is constant for all the resulting cells of the 

 organism. 



The two daughter-cells are each at first smaller than the mother-cell, but they 

 soon grow, and the process may recommence and be repeated in them, and in this 

 way cell-multiplication maybe exceedingly rapid. The cells, as is most generally the 

 case, may become entirely separated, but in some cases they remain in partial 



Fig. 221. MULTINUCLEATED CELLS FROM THE MARROW. HIGHLY MAGNIFIED. (E.A.S.) 



a, a large cell the nucleus of which appears to be partly divided into three by constrictions ; 6, a 

 cell the enlarged nucleus of which shows an appearance of being constricted into a number of smaller 

 nuclei ; c, a so-called giant-cell with many nuclei ; d, a smaller cell with three nuclei ; e i, other 

 cells of the marrow. 



conjunction, united by filaments of protoplasm which vary in number, length, and 

 thickness. 



Sometimes, a multiplication of nuclei within a cell occurs withoxit immediate 

 separation into new cells, as in the large cells which are found in the medullary 

 cavities of bone (fig. 221). 



Instances have been observed out of the body in which the amoeboid movements 

 of the protoplasm seem to have produced cell-division (Klein, Eanvier), but this 

 occurrence is seldom, and most likely abnormal ; indeed, it is found, as a general 

 rule, that whilst cell-division is proceeding, the external manifestations of activity 

 of cell-protoplasm cease almost entirely. 



The following are the more important phases of change of the chromoplasmic 

 filaments put in tabular form : 



Resting 1 condition of mother-nucleus. 



Close skein of fine convoluted filaments. 



Open skein of thicker filaments. Achromatic spindle 



seen within nucleus. 

 Movement towards middle of nucleus, and cleavage 



of filaments (which are usually V-shaped). 

 Stellate arrangement of V-filaments in equator of spindle. 

 Separation of cleft filaments, and movement along fibres 



of spindle. 

 Conveyance of V-filaments towards poles of spindle. 



NETWORK OR EETICULUM 1 . 



2. 

 SKEIN OR SPIREM .., ... ^ 3. 



CLEAVAGE 4. 



STAR OR MONASTER 5. 



DIVERGENCE OR METAKINESIS 6. 



DOUBLE STAR OR DYASTER... 7. 



