NUMBER OF OVA: ALBINO RAT 437 
My own observations on the rat naturally show some slight 
difference in the age periods from those given by Kingery. In 
the rat the first appearance of the newly formed follicles is at 
about ten days after birth, and their number increases until about 
sixty to seventy days, at which age as a rule ovulation occurs; 
but this process continues at least to the age of one year, though 
not as rapidly as before. 
The problem as to the origin of the definitive ova is not yet 
definitely settled. Some authors, Jenkinson (713), Kirkham 
(16), d’Hollander (04), and Sonnenbrodt (08), stated that the 
definitive ova are formed from the primordial germ cells, though 
some observers, Dustin, Karchakewitsch, Allen and Skrobansky 
(cited from ‘‘Oogenesis in the white mouse,” 717), Winiwarter 
and Sainmont (’08), consider that the primordial germ cells 
mainly degenerate, and thus, as the rule, the definitive ova can- 
not be produced from these. Kingery holds the opinion that the 
definitive ova are developed from the primary follicles formed 
after birth, but he did not state clearly the relation between the 
primordial germ cells of other authors and the definitive ova of 
his own designation. 
There is not much literature on the new formation of the egg 
cells after birth. Van Beneden (’80) described in the adult bat 
the egg cells as formed from the germinal epithelium. Lane- 
Claypon (05), in the ovary of the rabbit, concluded that the fol- 
licle cells and the interstitial cells are formed from the germinal 
epithelium. These interstitial cells, from their origin, are po- 
tential egg cells, and under the proper stimulus, are capable of 
developing into ova. Von Winiwarter and Sainmont (’08) stated 
that in the cat, at about the age of three and one-half to four 
months, a renewal of the activity (the third proliferation) of the 
germinal epithelium produces a new supply of germ cells which 
develop into the definitive ova, when all the egg cells of the first 
(embryonic) and second (shortly after birth) proliferations have 
degenerated; and he stated further (’08) that these definitive ova 
come either entirely from the third proliferation or partly from it 
and partly from the undifferentiated cells left over from the sec- 
ond proliferation. 
