A Comparative Study of the Structuie and Origin of the Yolk Nucleus. 665 
It is lioped that no serious mistakes have been made in quoting the 
views of writers to wkose works I have had access. The aim has been to 
give their own words, though it is realized that a false impression may 
even then be conveyed, when the extract is separated from wliat precedes 
and what follows. 
My own observations, I relate in a separate chapter, to avoid the 
confusion which one experiences in tfying to select the author’s own 
work from the mass of quoted material. 
To meet the requrrement of the Prize Committee, my own work is 
referred to in the third person. 
Historical: — The name yolk nucleus, is applied to a body or bodies 
found in the cytoplasm of eggs, differing somewhat from the rest of the 
cytoplasm. The following are some of the Synonyms that have been 
used — the body of Balbiani, Dotterkern, and paranucleus. Milne 
Edwards called it the embryonic vesicle, and Balbiani used the same 
term. 0. Schultze called it the vitelline nucleus; Munson called it the 
vitelline body, and cytocenter; and recently it has been called the egg 
centrosome and sphere. 
The first account of the yolk nucleus seems to have been published 
in 1845 by von Wittich (97), in his Inaugural Dissertation. He published 
a second paper (98) on the subject in 1849. This being only a few years 
after the publication of the cell theory by Schleiden and Schwann, 
and fifteen years before Max Schultze gave us our present definition of a 
cell, and a similar period before Gegenbaur(28) suggested the cell nature 
of the egg, a correct interpretation of this body could not be expected. 
The entire literature on this subject, very considerable in amount, 
has with some notable recent exceptions, chiefly an historical value. But 
it is none the less interesting, in the light of modern cytology, when viewed 
in connection with recent views concerning heredity, cell Organization, 
isotropism, epigenesis and preformation. It also touches the problems 
of the function of the nucleus, and its relation to the growth and differen- 
tiation of the cytoplasm. 
As early as 1848, Siebold (84) said: “Merkwürdig nehmen sich die 
Eier von Lycosa, Thomiscus, Dimedes, Salticus und Tegeneria aus, indem 
sie außer dem Keimbläschen, so lange sie noch nicht vollständig mit 
Dotter angefüllt sind, noch einen besonderen runden Kern von feinkörniger, 
aber fester Beschaffenheit enthalten.” He makes the interesting Observa- 
tion that layers detach themselves from its surface, without any per- 
ceptible diminution of its size. His belief that the yolk nucleus plays 
an important role in the development of the egg, based on the Observation 
