Embryology. 



129 



I will quote the following description of them, because, 

 for terseness combined with lucidity^ it is unsur- 

 passable. 



Researches, chiefly due to Flemming, have shown that the 

 nucleus in very many tissues of higher plants and animals con- 

 sists of a capsule containing a plasma of" achromatin," not deeply 



Fig. 36. — Karyokinesis of a typical tissue-cell (epithelium of Sala- 

 mander). (After Flemming and Klein.) The series from A to I 

 represents the successive stages in the movement of the chromatin 

 fibres during division, excepting G, which represents the "nucleus- 

 spindle" of an egg-cell. A, resting nucleus; D, wreath-form; E, 

 single star, the loops of the wreath being brolcen ; F, separation of 

 the star into two groups of U-shaped fibres ; H, diaster or double 

 star; I, completion of the cell-division and formation of two resting 

 nuclei. In G the chromatin fibres are marked a, and correspond to 

 the "equatorial plate"; b, achromatin fibres forming the nucleus- 

 spindle; f, granules of the cell-protoplasm forming a "polar star." 

 Such a polar star is seen at e.ach end of the nucleus-spindle, and is 

 not to be confused with the diaster H, the two ends of which are 

 composed oi chrotnatin. 



Stained by re- agents, ramifying in which is a reticulum of " chro- 

 matin " consisting of fibres which readily take a deep stain. 

 ( Fig. 36, A). Further it is demonstrated that, when the cell is 

 about to divide into two, definite and very remarkable move- 

 ments take place in the nucleus, resulting in the disappearance 

 of the capsule and in the arrangement of its fibres first in the 



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