274 Dixon . — The Possible Function of 
nucleoli and chromatin, when judged by Hertwig’s criteria, 
has no inherent objections ; while with regard to the equiva- 
lence of the male and female hereditary masses and the pre- 
vention of the summation of hereditary substance. I venture 
to think it offers some advantages over the generally received 
hypothesis, of which it is an extension. 
As additional support of this view some other phenomena 
may be quoted. Thus the diminution of chromatin and the 
relatively large amount of nucleolar substance observable in 
the nuclei of mature tissues is just what we would expect, if 
the chromatin-thread contains the hereditary substance which 
actually decides the properties of the mature cell, while the 
nucleoli contain the other — inactive in that special cell — 
hereditary properties of the species. That these latter must 
be present in the nuclei of mature cells is rendered necessary 
by the observed phenomena of regeneration 1 . 
The relatively small quantity of chromatin and the large 
amount of nucleolar substance in mature tissues seems to have 
been already remarked upon by Rosen 2 . He, however, 
believes that the nucleolus increases in importance with the 
gradual diminution of the chromatin ; whereas, according to 
the proposed view, it contains the dormant idioblasts, or 
hereditary units, gradually increasing in number with the 
specialization of the cell. The chromatin, on the other hand, 
as the cell specializes, is reduced in quantity until the idioblasts 
representing the special properties of the mature cell are alone 
present in its substance. It may not, perhaps, be out of place 
to point out that the great surface of the thread-like chromatin, 
compared with the small surface exposed by the spherical but 
much more bulky nucleolar substance, favours the view that 
the chromatin may be composed of the active idioblasts of 
the nucleus. Although this statement of the relative amounts 
of chromatin and nucleolar substance holds good in a number 
of cases, yet there are undoubtedly instances in which there 
1 Hertwig, 1 . c., p. 346 ; and ‘ Praformation oder Epigenese ? ’ Eng. trans. p. 47 : 
see also Wilson, 1 . c., p. 31 1. 
2 Rosen, Cohn’s Beitrage, 1895, p. 305. 
