DR. NELSON ON THE REPRODUCTION OF THE ASCARIS MYSTAX. 
575 
As soon as the ovule enters the glandular portion (Plate XXX. fig. 90 c, d) it 
floats free in a clear fluid secreted by the cells lining the oviduct. The ovule be- 
comes thicker and more rounded, losing the flattened form it assumes that of an 
oblong sphere (Plate XXVIII. fig. 52). A granular chorion (fig. 54/*) begins to form, 
surrounding the ovule and constituting an elastic shell (fig. 55 f). While this external 
chorion is forming, however, the internal contents are undergoing change, the vitelline 
granules become much smaller in size (fig. 52 c), the germinal vesicle and spot dis- 
appear, and in their place we find a number of large transparent globules (fig. 53 e), 
having much more the appearance of oil than of being formed by cells. These glo- 
bules are apparently formed partly by the disappearance of the germinal vesicle, and 
partly by the separation of the oil from the granules of the vitellus. After a time 
these oily globules (fig. 54 c) approach the circumference and disappear (fig. 55 e), 
while the minute opake particles (figs. 54, 55 c) pass towards the centre. The ovule 
now begins to shrink, the choi ion becomes more granular and thicker (fig. 56 f), while 
from its inner surface a delicate membrane separates (fig. 57 o), and contracting on 
the particles contained within it, forms one molecular mass, spherical and perfectly 
opake (fig. 56 o). 
This false ovum (fig. 56), if I may be allowed to call it so, is surrounded externally 
by a peculiar granulated chorion or shell of an irregularly ovoid form (fig. 56 /'), 
within which, but separated from it by a clear fluid, is the opake spherical mass 
already described, with its delicate membrane (fig. 56 o). On rupturing one of these 
false ova, the opake mass is found (fig. 57 c) to consist of granules and a few oil-glo- 
bules. While the fertile egg does not remain stationary but advances, stage after 
stage, till the worm is produced, the false ovum undergoes no further development, 
but when expelled from the vagina of the Ascaris rapidly decays. 
In all those instances in which the spermatic fluid was imperfectly developed, or 
had not ascended higher than the uterus, false ova alone existed (fig. 56), having all 
the characters of those just described, and incapable of further change. 
From this we may infer, that after tlie formation of the chorion (figs. 54 to 56/") 
impregnation of the ovule is impossible ; and as the chorion is formed while the egg 
is yet within the oviduct (Plate XXX. fig. 90 c, c?), fertilization must take place, if at 
all, while the ovule is still in the oviduct, and before the formation of that envelope. 
Let us now return to the fertile condition of the female, and trace the development 
of the ovum as it threads the oviduct (fig. 90 c, d). 
The ovula are here surrounded by the spermatic particles ; here it is that fecunda- 
tion takes place, — by whicli alone fertile ova can be produced. 
This conversion of the ovule into the fertile ovum, I shall endeavour to describe 
according to my own repeated observations. 
Immediately that the ovule passes the constriction which terminates the ovary and 
enters the oviduct (Plate XXVII. fig. 42 «), it comes in contact with the semen 
(fig. 42 />), and a marked change in its form and appearance takes place. It is at this 
