90 
V. H. Blackman. 
THE NUCLEUS AND HEREDITY. 
By V. H. Blackman. 
N AGELI, in 1884, by the help of his theory of idioplasm, was 
the first to give precision to the discussion of the question of 
the mechanism of inheritance. In his “ Mechanisch-physiologische 
Theorie der Abstammungslehre” he suggested that the two germ-cells 
both possess two kinds of protoplasm. One kind, which is possessed 
by them both in equal quantities, is the carrier of the hereditary 
qualities; while the other is present in abundance in the egg, but in 
the male cell occurs only to a minimal extent or may be absent 
altogether. The first he called idioplasm ; the latter is the ordinary 
protoplasm concerned mainly with metabolic processes. This dis¬ 
tinction of “ plasms ” in the sexual cells seemed to him to be the 
simplest explanation of the two facts, (1) that offspring as a whole 
resemble equally the two parents, (2) the great difference in bulk of 
the two sexual cells which is found in the higher plants and animals. 
Nageli’s theory was only a speculation concerning a presumably 
invisible differentiation of protoplasm. In 1884, however, it was 
given a possible morphological basis by Oscar Hertwig and 
Strasburger. These two observers had been working on the 
phenomena of fertilisation in animals and plants respectively. As a 
result of their observations they were led, quite independently, to the 
view that the nucleus is the carrier of the hereditary properties, and 
that its substance, especially its chromatin, must be identified with 
the idioplasm of Nageli. This view was soon accepted by many 
workers, such as Weismann, Kolliker, de Vries, Roux and Boveri, 
and proved itself a stimulating working hypothesis. 
The grounds on which this view has won acceptance by so 
many biologists may be briefly summarised as follows. First, there 
is the equivalence of the nuclei of the male and female cells in 
fertilisation, shown in many cases by the fact that the two 
nuclei bring in equal number of chomosomes. Secondly we have 
the special phenomena of mitosis, in which the nuclear material is 
so carefully divided into, apparently, exactly equal and equivalent 
halves. Such a process does not seem intelligible unless it is 
conceived as a mechanism for the equal distribution, qualitatively 
and quantitatively, of the hereditary material. Thirdly we have the 
close relation'of the processes of fertilisation and nuclear reduction. 
