A Comparative Study of the Structure and Origin of the Volk Nucleus. 697 
vermindert.” He seems to regard the degeneration as due to absence 
of a nucleolus. Instead of it, there are in the germinal vesiele irregulär, 
shining, striated, crystalline bodies. Both the germinal vesiele and the 
yolk may undergo the same change. 
Pflüger (71) referring to the egg of the cat and of the cow, says 
that a cat becomes ten years old; and during that time, at most two 
hundred eggs have left the ovary, while in youth several thousand were 
present. Therefore very many must have degenerated. Physiology, he 
says, must regard this as normal; for, in order that one folliele may develop, 
several must perish; for all would perish, if nature allowed all to be equally 
developed. He refers to fatty degeneration as follows: “Durch die beschrie- 
bene fettige Entartung werden die Follikel mit Epithel und Ei ergriffen; 
allmählich klärt sich das Gewebe des GRAAFschen Bläschens wieder auf ; 
seine Struktur ist aber undeutlich geworden, und schließlich deuten nur 
hellere, runde Flecken die Stelle an, wo ein Follikel lag.” He says the yolk 
is often in the form or balls or spheres resembling cleavage cells. The 
yolk dissolves. The most interesting cause of this was cells. They were 
found attached to the yolk balls. He describes these as granulosa cells, 
that send processes through the zona where thev are connected inside 
the egg with vesicles. As the peripheral yolk dissolves, these inner vesicles 
become loosened and lead an independent existence. He observed this 
in eggs of cats from four to ten months old, and in a certain sense, he con- 
siders it normal. “Es handelt sich also hier um die eigentümliche Tatsache, 
daß eine im Grund krankhafte Erscheinung als notwendiges Glied in das 
Bereich des gesunden Lebens sich einfügt.” 
Schneider (81) gives an extended account of degeneration of egg 
and sperm cells in leeches, birds, mammals and other animals. He says 
it occurs in fishes and amphibia. According to him degeneration of the 
egg is most apt to occur in those animals in whic-h the period of Opposition 
is limited to a definite period of the year. In eggs carried over from 
one season to the next, degeneration may take place, by fatty degenera- 
tion and by inwandering leucocytes. He says: “Diese Zellen setzen sich 
nun an die von dem Eierstock abgelösten Eier und dringen in dieselben 
ein. Das erste Eindringen kommt selten zur Beobachtung . . . Nach 
und nach dringen mehr Zellen in das Ei, welche darin wachsen, fressen 
und sich mit kleinen Körnchen und einem größeren fettartigen konturierten 
Körper füllen. Das Ei zerfällt immer mehr, es bilden sich scharf umschrie- 
bene Ballen darin, welche ungefähr wie Furchungskugeln aussehen. End- 
lich wird die Membran faltig und schließlich wird sich das ganze Ei wohl 
auflösen.” 
