Ill 



and are lying in salt solution the membrane may remain intact for more 

 than three clays. The toughness and firmness of this nuclear membrane is 

 of interest in connection with the question of the extrusion into the 

 cytoplasm of certain chromatin masses is the nucleus, to be described 

 a few paragraphs below. 



A very dehcate linin net with nodal granules is present, resembling 

 exactly in structure and staining reactions the cytoplasmic net and gra- 

 nules. The real structure is that of a foam, at least in the »resting« 

 nucleus. 



The chromatin net in the »resting« nucleus consists of large and 

 small chromatin masses and their branching anastomosing pseudopodia- 

 like processes. In certain conditions of the nucleus no such processes 

 are found. 



As division approaches , the longitudinal fibres of the linin net be- 

 come emphasized, the transverse fibrils becoming less numerous and 

 fainter. These longitudinal fibrils do not form a true spindle or any 

 very marked or definite structure. The chromosome branches which run 

 longitudinally are likewise seen to be thickened , while the lateral bran- 

 ches are drawn in or become much fainter. In nuclei stained with sa- 

 franin and light green the distinction between these two kinds of fibrils 

 (linin and chromatin fibrils) is very sharp and clear, the former being 

 green and the latter red. 



There is no clear equatorial plate of chromosomes at any stage, but 

 one sees irregularly dumb-bell-shaped masses of chromatin (chromosomes) 

 at the equator, just inside the nuclear membrane. These soon comple- 

 tely divide, except for connecting threads of chromatin, and the halves 

 migrate to the two poles of the nucleus. As the daughter chromosomes 

 pass toward the poles each is seen to be united to the pole by a thread 

 of chromatin which grows thicker as it shortens during this migration. 



No centrosomes are present inside or outside the nucleus, nor is 

 there anything of special note at the poles of the nucleus. Achromatic 

 granules are usually present here as they are throughout the nucleus, 

 but there is generally no special aggregetion of them. 



I have found no longitudinal division of the chromosomes, though 

 Teichmann so interpreted and figured some of his preparations. The 

 chromosomes are never compact and regular, but always remain more 

 or less branched. They are best seen during the migration stages of 

 mitosis and are then found to be eight in number (fig. 1). They differ 

 in size and shape and in the number of chromatin granules they contain 

 and these differences may be constant. The chromosomes at all times 

 lie just inside the nuclear membrane, never near the center of the nucleus. 



As the daughter nuclei are formed the chromosomes send out thin, 



