NUMBER OF OVA: ALBINO RAT 459 
this new formation becomes less active, though it may continue 
for a year after birth (chart 2). 
9, The primitive ova, which are present during foetal life, are 
found degenerating immediately after birth. The rate of de- 
generation rapidly diminishes from birth to three weeks of age, 
but continues up to sexual maturity, at a slower rate. The exact 
period of degeneration of definitive ova is not known, but proba- 
bly it begins before puberty, and after puberty the degenerate 
follicles are derived principally from the definitive ova. In the 
rat about four weeks old the medium-sized follicles show degen- 
eration, and in general the number of degenerated follicles of 
large size is more than one and a half times that found before 
puberty. The converse relation is true in the case of small fol- 
licles. The mean number of all degenerated follicles is about. 10 
per cent of the total number of ova. 
10. Ovulation can occur spontaneously, independent of sexual 
intercourse and without the influence of the male sex. Well- 
developed follicles appear as early as twenty-six days after birth. 
These follicles contain ova with a diameter of 60 ~—equal to 
those found in well-developed mature follicles. Should some 
special stimulus be deemed necessary for the discharge of the 
ovum, it is suggested that either the ovary itself or some other 
ductless gland might furnish such an hypothetical stimulating 
substance. 
11. The body length of rats was found a better criterion for 
the first appearance of corpora lutea than either age or body 
weight. The corpora lutea are found in rats between 148 to 
150 mm. in body length (table 18). 
12. The corpora lutea formed in rats in which the ova have 
been fertilized are a little larger than those in non-fertilized rats. 
It is stated that usually eight to ten ripened ova are discharged 
at the same time. We found, however, that near maturity there 
may be as many as twenty-one follicles in both ovaries. 
