272 H. LYNDHUKST ]>UKE. 



chromatin masses and the breakint^ up of the karyosome 

 have proceeded for some time, a new structure appears in 

 the nucleus. In close proximity to the main karyosome 

 I'esidue, Avhich is seen lying near the periphery of the nucleus, 

 an ill-defined mass appears "which takes up nuclear stains 

 very definitely. The earliest appearance of this mass is shown 

 in fig. 9 before the chromidia formation has progressed very 

 far. A slightly later stage is shown in figs. 10 and 11, where 

 the nuclear area presents a homogeneous appearance, without 

 any signs of the chromidial elements being discernible, while 

 the neighbourhood of the main karyosome residue is occupied 

 by a somewhat elongated mass, showing faint longitudinal 

 striation (fig. 11). The relative size of this mass, which I will 

 call the " achromatic mass,"^ is shown in figs. 9, 10, 11. It will 

 be noticed that the various products of the karyosome are in 

 close connection with it. 



At this stage, the absence in my preparations of any 

 structures distinguishable as definite chromosomes or cen- 

 trosomes is to be emphasised. The achromatic mass stains 

 deeply with iron-haematoxylin, but yields to the differentiating 

 iron-alum before the karyosome and its products become 

 decolorised. 



The next stage in the division represented is shown in figs. 

 12 and 13. The achromatic mass has increased in bulk and 

 definition, and has become more drawn out. The striation is 

 very marked, and for the first time in the course of the division 

 the true chromosome element appears. At each pole of the 

 achromatic mass, which is now distinguishable as a true 

 spindle, there is a small black mass of chromatin ; while 

 converging towards this mass, like the ribs of a basket, are 

 seen deeply stained streaks of g'ranules of chromatin, arranged 

 upon the spindle-fibres and obviously en route for the re- 

 spective poles of the figure. It may here, again, be seen 

 that the spindle stains very deeply with chromatin stains, and 



1 I call this stnictiire the " achromatic mass "' because of its function 

 — as seen in its hiter development — and not on account of its staining 

 properties. 



