Oogenesis in the white mouse

unaccompanied by figures, and therefore can not be considered conclusive. Jenkinson devotes a few pages in his book to this question, but is hardly convincing. It would seem that, in the mouse, there are three possible courses of development open for the ‘primordial germ cells’ :1) they may persist and form the primitive germ cells or oocytes and so eventually degenerate; 2) they may, after reaching the permipal epithelium, develop into the definitive germ cells; or, 3), they may degenerate completely. The evidence presented, J think, shows that neither the first nor the second is the course followed. The objection mentioned above, that no one has traced these cells through to mature ova, also disposes of the second possibility. There is, indeed, the further possibility that the ‘primordial germ cells,’ after entering the germinal epithelium, lose their size and characteristics and become indistinguishable from the mesathelial cells. It would be extremely difficult to prove or disprove this, but the burden of the proof would, it seems to me, rest upon any one who supOOGENESIS IN THE WHITE MOUSE 287 ported such a view. The last course, degeneration, seems to be the most probable fate of these cells. There are not.many examples in the literature of a new formation of egg-cells after birth. Van Beneden (’80) described in the adult bat a formation of egg-cells from the germinal epithelium. From his description and figures, the process resembles the formation of oocytes in the mouse before sexual maturity; but, as he did not connect this process with that in the embryo, it is difficult to say whether it is strictly comparable with the condition in the mouse. Lane-Claypon (’05), in a study of the ovary of the rabbit, concludes that from the germinal epithelium are formed defini-. tive ova, follicle cells, and interstitial cells. These interstitial cells, from their origin, are potential egg-cells, and, under the proper stimulus, are capable of developing into ova. In this case, the proper stimulus is provided in some way by pregnancy, and a number of these cells become differentiated into oocytes. Apparently these conclusions have not been confirmed by other authors, and hence lpse something of their force. Von Winiwarter and Sainmont (’08) state that in the cat, a t about the age of three and one-half or four months, a renewal of the activity of the germinal epithelium provides a new supply of germ cells which develop into the definitive ova, when all the egg-cells of the first and second proliferations have degenerated. In a note appearing about the same time (’08*), they state that these definitive ova come either entirely from this third proliferation, or partly from it arid partly from undifferentiated cells left over from the second.5 6 “Es tauchen nun jctzt in den Epithelhaufrn und Strangen dcr Corticalis Kleinc Gruppen von Zellen auf, dcrcn l ieme in] Stnubformiyen oder dcutobrochen Stadium sind. Dicse Forrnen waren schon seit langer Zeit nicht mehr vorhanden, und da sic den ersten Stufen des Wachstums des Oocyten cntsprcchen, ist es augenscheinlich, dass sic niit cincr Ncubildung von Eiern zusammenhnngen. Wir glauben bewiesrn zu haben, dass in Saugetierovarium nicht nur samtlichc Markstrange, sonderu auch alle Eier und Follikcl dcr primitivcn Corticalis dem Untergang anheimfallen. Die definitivcn Eier entstammen entweder von undifferenzierten Zellcn der mei ten Proliferation (Pflugcrsche Schlauche) oder von Zellen der dritten Wucherung oder invaginations 6pith6lials Es ist uns nicht moglich, wenigstens morphologisch, die Elcmentc der eincn und andercn zu unterscheiden. ” (v. Winiwarter and Sainmont, ’08 a, p. 616.)