

‘Ovulation and Degeneration of Ova in the Rabbit. 261 
the ovarian tissue, which consists essentially of a connective tissue network 
enclosing large parenchyma cells, through which blood vessels run. In the 
region of the follicle this tissue is somewhat modified. Close round the 
basement membrane I find a thin layer of parenchyma cells in a connective: 
tissue network, the theca interna, and immediately outside that the con-. 
nective tissue itself is specially developed into closely approximated fibrous. 
bands with a few parenchyma cells in the interstices thereof—the theca. 
externa (Nos. 23, 29, 30, 33). 
The first sexual season begins in the domestic rabbit as a rule in February 
or March, but is dependent somewhat on the food given, on the warmth and 
shelter provided, and on the frequency with which they were allowed to: 
produce young the previous year. 
Prior to that time certain of the Graafian vesicles enlarge, a space con- 
taining liquor folliculi appears, and the ovum, surrounded by a thickened mass 
of epithelial cells (the discus proligerus) lies eccentrically but connected: 
with various portions of the follicle wall by strands of this tissue. The 
remainder of the epithelium round the wall of the follicle is much reduced in 
thickness. The growth of those vesicles situated near the surface of the 
ovary causes them to project and form swellings on the surface; both the wall 
of the follicle and the tunic of the ovary is here very much attenuated, so: 
much so that in some of them, when ripe, the structure is sufficiently 
transparent to allow of the ovum being seen within the vesicle. During 
procestrum, the blood vessels which surround these follicles become more 
numerous, enlarged and congested, and such as run in the thin wall which 
projects on the surface of the ovary give these follicles the bright pink colour 
which is characteristic of them. 
It is important to notice, however, that a brilliant suffused red colour does 
not denote a ripe Graafian vesicle but, as I will show below, a degenerate 
follicle which will not rupture; failure to distinguish between these two 
appearances has been the cause of much error: 
Maturation of the Ovum.—Normally, immediately after copulation the ripe 
ovum in the swollen Graafian follicle is affected. The cells of the discus 
proligerus, which until now had closely invested the ovum, begin slowly to 
withdraw (cf. 19). During the growth of the ovum nutriment is supplied to 
it by the aid of these cells; as I have already shown (No. 12), protoplasmic 
processes from them are projected into the radiating canals of the zona radiata ; 
now the cells withdraw radially and eventually remain attached to the zona 
only by these exceedingly fine strands. This process apparently occupies 
some hours. At the same time the ovum, bounded by its thin vitelline 
membrane, withdraws somewhat from the zona leaving a narrow space 
