270 Dixon . — The Possible Function of 
substance is distributed between the chromatin-thread and 
the nucleoli. This distribution is so arranged that the units 
of hereditary substance, idioblasts (Hertwig) or pangens (De 
Vries), which determine the attributes of the cell in which the 
nucleus is actually situated, are located in the chromatin- 
thread, while the inactive or dormant idioblasts are contained 
in the nucleolus or nucleoli. 
As will be seen, this view involves no differential division 
of the germ-plasm during cell-division such as Weismann 
assumes, but is in accordance with the views on heredity held 
by De Vries, Hertwig, and Driesch. If, however, we wish to 
express it according to Weismann’s theory of the germ-plasm, 
we may regard the chromatin as containing the active, the 
nucleolus the inactive or latent determinants, of which, even 
according to Weismann, there must be some in the nucleus 1 . 
Hertwig 2 says, ‘In order to establish the hypothesis that 
the nucleus is the transmitter of the elemental germs, four 
points have to be considered : — 
‘1. The equivalence of the male and female hereditary 
masses : 
1 2 . The equal distribution of the multiplying hereditary 
mass upon the cells which are derived from the fertilized 
ovum : 
‘3. The prevention of the summation of the hereditary 
masses : 
‘4. The isotropism of protoplasm.’ 
These criteria may also be used to test the proposed view 
of the hereditary function of the chromatin and of the 
nucleoli. 
In recent years the opinion that the substance of the 
nucleoli is distributed along the chromosomes during the 
early stages of karyokinesis has been steadily gaining ground. 
The evidence in favour of this view is chiefly based on 
observations of the simultaneous change in the amount of 
nucleic acid in the chromatin and nucleoli. When the amount 
1 Germ-plasm; Eng. trans., p. 103. 
2 The Cell; Eng. trans., p. 345. 
