IV] 



AND STRUCTURE OF THE CELL 



305 



1. The chromatin, which to begin with had been dimly seen as 

 granules on a vague achromatic reticulum (Figs. 89, 90) — perhaps no 

 more than an histological artefact — concentrates to form a skein or 

 spireme, often looked on as a continuous thread, but perhaps 

 discontinuous or fragmented from the first. It, or its several 

 fragments, will presently spht asunder; for it is essentially double, 

 and may even be seen as a double thread, or pair of chromatids, from 

 an early stage. The chromosomss are portions of this double thread, 

 which shorten down to form httle rods,' straight or curved, often 



chromoaome* 



Fig. 90 A. 



Fig. 90 B. 



bent into a V, sometimes ovoid, round or even annular, and which 

 in the living cell are frequently seen in active, writhing movement, 

 *"hke eels in a box"*; they keep apart from one another, as by 

 some repulsion, and tend to move outward towards the nuclear 

 membrane. Certain deeply staining masses, the nucleoh, may be 

 present in the resting nucleus, but take no part (at least as a rule) 

 in the formation of the chromosomes; they are either cast out of 

 the nucleus and dissolved in the cytoplasm, or else fade away in situ. 



* T. S. Strangeways, Proc. E.S. (B), xciv, p. 139, 1922. The tendency of the 

 chromatin to form spirals, large or small, while the nucleus is issuing from its 

 resting-stage, is very remarkable. The tensions to which it is due may be overcome, 

 and the chromosomes made to uncoil, by treatment with ammonia or acetic acid 

 vapour. See Y. Kuwada, Botan. Mag. Tokyo, xlvi, p. 307, 1932; and C. D. 

 Darlington, Mechanical aspects of nuclear division, Sci. Journ. B. Coll, of Sci. 

 TV, p. 94, 1934. 



