252 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
as the ovum has reached the size of one-hundredth of an inch the nucleus is obviously 
shifted from its central position. From this time onward the ova present much the 
same appearance till sometime after the period when they reach somewhat more than 
one-half the diameter of the mature egg. They then begin to show signs of pig- 
mentation which vary in amount, as already stated, in different individuals. This 
pigment, like that found in the ovum of the frog, is mostly superficial in its distribu- 
tion and consists of minute granules, uearly opaque, which form a thin stratum just 
beneath the egg membrane and embedded in the superficial protoplasm. This pig- 
ment is also finally distributed, in varying quantity, at different points at the surface 
of the egg, so that the darkened discoidal germinal area is marked out by it, as shown 
in Figs 1 and 2. This definite distribution of the pigment is accomplished by the 
time the ovary reaches its maturity when the whole organ assumes its characteristic 
dark color, due to the presence of the pigment in the individual eggs. 
Sections of the mature roe show that each egg is inclosed in a vascular capsule or 
follicle in which it reaches its full size. A thick homogeneous egg. membrane is de- 
veloped just external to the pigmented layer of the ovum. This membrane resists 
the action of carmine and remains colorless when treated with an alkaline solution of 
that dye. A layer of substance just external to the egg membrane and of about the 
same thickness is readily stained by carmine. This outer layer is the partly soluble 
glairy substance by means of which the ovum adheres to foreign bodies, and which 
finally hardens and cements them firmly to whatever they touch. The next layer is 
the vascular capsule or follicle which is traversed by a delicate plexus of capillary 
vessels which nourish the maturing ovum. This follicle is finally ruptured when the 
ovum drops into the abdominal cavity, from which it escapes by way of the genito- 
urinary passages presently to be described. 
The ovaries, after the ova have been discharged from their follicles, present a 
shredded or torn appearance. This is due to the presence of the great number of col- 
lapsed egg follicles and to the more or less degenerate vessels which traverse the 
stroma or supporting substance of the tissue of the ovary, and which are undergoing 
retrogressive changes. These retrogressive processes, after the ova which have been 
matured for that season have been set free, go on until the ovary again contains 
nothing but verj^ immature eggs, each of which must grow greatly in size in order to 
bring up the ovary to the size it had reached before ovulation began. Since the 
“ spawning,” as the process of ovulation is called, takes place but once a year, it is 
clear that it is a periodic phenomenon, just as the process of ovulation is even amongst 
higher animals. There is a period of preparation for the business of ovulation, and 
this begins for the next year with the cessation of the process for the preceding sea- 
son. This preparation involves the collapse and diminution of the caliber of the blood- 
vessels which have supplied the ovary during its period of greatest functional activity, 
and also the absorption of the ruptured follicles in which the last crop of ova were 
matured. 
Some few mature ova do not seem to be discharged at all, but undergo absorption 
within the follicle, together with their enveloping membranes or zonse radiata, and 
glairy coverings of mucigen. Such degenerating ova, in sections of the “ spent” recu- 
perating roe, are found to contain a large yolk mass somewhat irregular in form and 
thrown into folds or wrinkles superficially with the pigment granules not aggregated 
at the surface, but irregularly distributed throughout the substance of the yolk mass. 
