A Comparative Study of the Structure and Origin of the Yolk Nucleus. 693 
mon in the animal kingdom, bnt they do not pretend to give any further 
explanation of it. 
Interesting, also, in its bearing, first on the question of origin and 
nature of the yolk nucleus, second in its bearing on parthenogenesis, but 
mainly because it shows to what extent Interpretation of observations 
is influenced by the larger problems prominent at the time, is the work 
of Stuhlmann (86). He says: “Es ist mir nun gelungen, an einer Reihe 
von Insekteneiern sicher einen Austritt von großen Ballen aus dem Keim- 
bläschen zu konstatieren, die sich nachher im Eiplasma auflösen. Später 
verschwindet das Keimbläschen vor unseren Blicken, bis wir endlich am 
oberen Eipol den Furchungskern wiederfinden.” Stuhlmann ealls atten- 
tion to the work of Grobben (30) and also to Weismann to show that 
maturation takes place in parthenogenetic ova. He seeks to show that 
the germinal vesicle in such eggs, behaves like an amoeba, giving out 
pseudopodia containing nucleoli and chromatin granules which are con- 
stricted off from the germinal vesicle, and appear for some time in the 
cytoplasm, as “Reifungsballen” and are finally dissolved. He also finds 
bodies resembling real nuclei near the periphery of the egg, which he 
admits may be derived from inwandering folliele cells. But they differ 
from the first named “Reifungsballen”. The latter give rise, in some 
eggs, to granulär masses, which he calls diffuse yolk nucleus, or they 
may give rise to one or two or more large spherical bodies, the true yolk 
nucleus. 
Stuhlmann (86) seems to believe that parthenogenesis is common; 
and that many eggs can develop partly parthenogenetically; in Support 
of which he cites Leuckart (49) on frog’s egg, Oellacher (69), Heus- 
mann, Jourdan (39) and Osborne (70). He seems to assume that the 
“Reifungsballen” are given off as a preparation for such development. 
He says: “Die Reifungsgeschichte der Eier von Banchus hat uns aber die 
interessante Tatsache ergeben, daß das Auftreten der Dotterkerne un- 
abhängig von dem Austritt der Ballen ist, da letzterer Vorgang ersterem 
hier vorangeht. Das sind entschieden voneinander ganz unabhängige 
Bildungen . . . Bei der Bildung des Dotterkerns konnten wir zwei Stadien 
unterscheiden: Zuerst werden kleinere Ballen in der Nähe des Keim- 
bläschens gebildet, welche dann später zu einem am hinteren Eipol liegen- 
den Dotterkern verschmelzen.” 
The entrance of chromatin substance from the nucleus into the vitellus 
has been affirmed by Fol, Roule, Will, Leydig, van Bambeke, Henne- 
guy, Schmidt, Kohlbrugge, Loyez and many others. Some of these 
also admit that yolk material from the folliele cells enters the egg. 
