the Nucleolus in Heredity. 2 77 
visible in it. After fusion a second large nucleolus appears 
in the nucleus of the ovum, presumably derived from the 
chromatin of the sperm-nucleus, as indeed the authors quoted 
state. If this be true, and if this nucleolus does not represent 
some of the hereditary substance contributed by the male 
nucleus, we can no longer admit the equivalence of the male 
and female hereditary masses in this case ; but we should be 
forced to believe that the female nucleus contributes much 
the greater share of hereditary substance to the embryo. As 
was seen above, a comparison of the amount of chromatin in 
the male and female nuclei before fusion led to a contradictory 
result. 
The transformation of nucleoli bodily into nuclei in the 
formation of the spores of Saccharomyces recently observed 
by Wager 1 appears to me to be an exceedingly strong 
argument in favour of the view here put forward. This 
observation I have been able lately to confirm by the discovery 
of a completely similar phenomenon in the development of 
the ascospores of Tuber aestivum . The spores of this 
Ascomycete are multinucleate. The formation of the spores 
takes place as follows : — The nuclei formed in the ascus are 
large and contain very finely granular chromatin, in which 
are imbedded a few nucleoli which are easily stained with 
the acid anilin-dyes. Round four or five of the nuclei, and 
in close proximity to their membranes, the cell-walls of the 
ascospores are developed. When thus enclosed the nucleus 
enlarges until it completely fills the cell. During its enlarge- 
ment the finely granular chromatin disappears, whilst the 
nucleoli increase in size and number until there are about 
eight in the spore. Simultaneously with their increase in 
number and enlargement, their colour-reaction changes, and 
from fixing the acid anilin-dyes, the nucleoli come to exhibit 
an affinity for the basic stains. They then lose their com- 
pletely homogeneous appearance and pass into a state 
resembling the dense minute nuclei of the hyphae of the 
Fungus, but they are larger and more granular than these latter. 
1 Wager, Ann. of Botany, Vol. xii, Dec. 1898. 
