RESEARCHES ON KARYOKINESIS AND CELL DIVISION. 37 



separating it from the cell substance. Flemming concludes 

 from tliis tliat the nucleus is composed of two substances, of 

 which one is stained by dyes the other not, and he accord- 

 ingly calls the former chromatin, the latter achromatin. He 

 believes that both of these substances are contained in each 

 element of the resting nucleus, while at the beginning of 

 karyokinesis all the chromatin is converted into fibrils, the 

 achromatin filling up the interstices between these and 

 forming the clear space round the fibrillar mass. 



The convolution, by a change in fhe arrangement of the 

 fibrils, passes into the "wreath" form (fig. 3), the bends being 

 arranged, Avith more or less regularity, round a central space. 

 After this the mass of fibrils, in which no free ends have 

 hitherto been visible, breaks up into a number of V-shaped 

 loops, each with a bend and two diverging limbs. These 

 arrange themselves with the bends placed centrally and 

 the limbs directed peripherally, forming a star (mother 

 star). Each of these loops, after it is formed divides itself, 

 according to Flemming, into two by a longitudinal splitting 

 of the fibril (fig. 5) ; but this statement is not accepted by 

 Klein (loc. cit.), who was unable to determine with the 

 highest powers whether the appearance referred to was due 

 to a longitudinal splitting or caused by the fibrils becoming 

 tubular. Flemming^ says that owing to this splitting the 

 loops become twice as numerous and only half as thick, and 

 that since the loops again become less numerous and thicker 

 after the formation of the daughter stars, a fusion of the 

 loops in pairs must occur at that stage. 



Up to the phase of the mother star the karyokinetic figures 

 are of three dimensions, and the diagrams represent optical 

 sections ; but in the next stage the loops begin to be com- 

 pressed towards the equatorial plane, so-called from its 

 relation to the nuclear spindle when this is present (fig. 6), 

 as in vegetable cells and segmenting ova of Echinodermata. 

 This movement Fleming has observed to be again reversed, 

 so that the figure recovers its previous form (fig. 7). He calls 

 the two stages of this movement " the systole and diastole - 

 of the star," and illustrates its character by diagrams which 

 are copied in figs. 34 and S5 ; the phenomenon does not 

 seem to have been noticed by other observers. Ultimately, 

 the loops form the characteristic " equatorial plate " (fig. 8), 

 in which the bends of the loops are directed away from the 

 equatorial plane, their limbs towards it. As the loops form 

 a broad ring, the space within which is empty, and as the 

 bends converge somewhat, they form on each side of the 

 ' "Beitrage," ii Theil, ' Archiv Mik, Anat.,' Bd. xviii, 1880, 



