438 HAYATO ARAI 
Kingsbury (713) inclines to the opinion that there is no evi- 
dence of a new formation of ova by the third proliferation of 
Winiwarter and Sainmont. Van der Stricht (’11) does not dis- 
cuss at all the new formation of ova, but simply states that in 
the adult ovary in cats the definitive ova are derived from the 
second proliferation. Felix (’12), in describing the development 
of the ovary in man, states that after the tunica albuginea is 
formed, in embryos of 180 mm. in length, no egg cells can be 
added to the interior of the ovary from the epithelial layer, and 
thus, according to this author, there is no possibility of a new 
formation of ova from the germinal epithelium. 
Kingery (717), in his studies on the white mouse, states that 
there is a new formation of germ cells after birth, and that the 
definitive ova come from the primary follicles. Briefly put, 
Kingery believes that at birth all the cells of the germinal epi- 
thelium seem equally capable of developing into oocytes, follicle 
cells or epithelial cells, though it is not evident just what factors 
are responsible for their eventual fate. As the ovary becomes 
more mature and the cells better differentiated, this potentiality 
of the cells of the germinal epithelium is lost, and after sexual 
maturity no more egg cells or follicle cells are derived from the 
epithelium. 
He states also that all the egg cells of the first or embryonic 
proliferation in the mouse undergo degeneration and disappear. 
In ovaries of mice, from about seventeen days after birth up to 
sexual maturity, and at the adult stage, egg cells in their folli- 
cles may be seen in various stages of degeneration and atresia. 
This is the evidence, of course, that a large number of these 
germ cells of embryonic origin degenerate and are resorbed. 
The degeneration of the definitive ova, which in all likelihood 
sets in before sexual maturity, is continued through the whole 
sexual life of the individual, as is well known. Since, then, a large 
number of definitive ova degenerate, and since these are situ- 
ated more superficially than the primitive germ cells, which are 
mostly degenerated, it seems reasonable to conclude that all the 
primitive germ cells degenerate and are resorbed, and that all 
the definitive ova arise after birth from the germinal epithelium. 
