MATURATION AND FECUNDATION OF THE OVUM. 113 
Examined with T ‘ T homogeneous immersion of Zeiss it is seen 
to be finely punctated, and the points are united by slender 
threads. The protoplasm is in fact, as has been discovered by 
many histologists in animal cells, made up of a reticulum of 
moniliform threads. There must be an interfibrillar substance 
filling up the meshes of the reticulum. 
Nothing is said upon the question whether the ovum is 
attached to the rhachis by the end of the tail of the mallet, or 
by some other point. This is a question of some importance, 
because in some animals, e.g. Lamellibranchs, the micropyle 
is formed by the pedicle of attachment of the ovum. 
Vitelline Membrane. — In the ova, already detached, 
taken from the lower part of the ovary, there is no vitelline 
membrane, so that in this animal the formation of the micro- 
pyle is not due to the presence of a pedicle of attachment. 
Meissner 1 has stated that in the nematode egg studied by him, 
the micropyle was formed in the way indicated, while other 
authors have denied the existence of any membrane before the 
entrance of the spermatozoon. In Ascaris megalocephala, 
although it is usually impossible to detach a membrane before 
the entrance of the male element, it is certain that the external 
layer of the vitellus has before that period become differentiated 
and resistant. Ova, when ready to receive the spermatozoon, 
do not flatten out in all directions as they do at an earlier stage, 
but the vitellus escapes at the pole of impregnation. Imme- 
diately after a spermatozoon has attached itself to the plug of 
impregnation a membrane is present which becomes separated 
from the parapolar region and the polar disc during preparation. 
In unfertilized females a membrane is formed round the ovum. 
It may be concluded then that the vitelline membrane is not 
formed in consequence of fecundation. 
The Germinal Vesicle, whose position in the ovum has 
already been indicated, appears in the fresh state as a clear 
space in the vitellus containing a dark spot, the germinal spot 
or nucleolus. 
In ova treated with osmic acid and picro-carmine (see fig. 1,P1. 
1 ‘ Z. f. w. Z..’ Bd. v, 1853. 
VOL. XXV. NEW SER. 
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