GERM CELLS OF ANURANS 283 
presented by merely a single group of vertebrates. The answer 
is, that scattered here and there through the hterature is consider- 
able evidence of an extremely suggestive nature, derived from 
study of the germ cells in widely separated groups of chordates, 
which, when taken in conjunction with conditions existing in 
anurans, suggest at once the working hypothesis stated above. 
Some of this evidence will be briefly reviewed here. 
In 1908 Von Winiwarter and Sainmont described two prohfera- 
tions of cells from the germinal epithelium of the cat ovary; the 
first formed the medullary, -the second the cortical cords. Ac- 
cording to their account, the germ cells and follicle cells of the 
first proliferation and the sex cells of the second all degenerate 
and disappear when the j^oung kitten is only a few months of 
age. About three and a half to four months after birth, the 
germinal epithehum of the ovary shows marked activity, and 
proHferates a third generation of germ cells, from which the 
definitive sex cells of the adult are derived. This third genera- 
tion forms the cortex of the ovary in grown animals. In a short 
paper published at nearly the same time as their monograph they 
state that the definitive ova of the sexually mature cat are derived 
either entirely from this third proHferation of the germinal epi- 
thelium, or else partly from it and from undifferentiated cells left 
over from the second prohferation, i.e., those that failed to degen- 
erate. For example, these authors state (p. 616) : 
Es tauchen nun jetzt in den Epithelhaufen und Striingen der Corti- 
calis kleine Gruppen von Zellen auf, deren Kerne im staubformigen 
oder deutobrochen Stadium sind. Diese Formen waren schon seit 
langer Zeit nicht mehr vorhanden, und da sie den ersten Stufen des 
Wachstiims des Oocyten entsprechen, ist es augenscheinlich, dass sie 
mit einer Neubildung von Eiern zusammenhangen .... Wir 
glauben bewiesen zu haben, dass in Saugetierovarium nicht nur samt- 
liche Markstrange, sondern auch alle Eier und Follikel der primitiven 
Corticalis dem Untergang anheimf alien. Die definitiven Eier ent- 
stammen entweder von undifferenzierten Zellen der zweiten Prolifera- 
tion (Pflligersche Schlauche) oder von Zellen der dritten Wucherung 
oder Invaginationsepitheles. Es ist uns nicht moglich, wenigstens mor- 
phologisch, die Elemente der einen und anderen zu unterscheiden. 
Now, oddly enough, all of the embryonic (primordial) germ 
ceUs described by Winiwarter undergo the characteristic nuclear 
