580 
DR. NELSON ON THE REPRODUCTION OF THE ASCARIS MYSTAX. 
that is first affected (figs, 64, 66 c), the process of disintegration gradually passing 
towards the centre. 
This mottled appearance (fig. 65) has been noticed by Reichert in the egg of a 
Strongylus, and ascribed by him to the formation of cells within the yolk, which is 
certainly not the case in the fertile ova of the Ascaris mystax. 
When there is much disintegration, the germinal vesicle may be seen with its 
germinal spot or nucleus (figs. 64 to 66 h, a), and occasionally within this (figs. 64, 65 a), 
again, another nucleolus (figs. 64, 65 h). 
But in general the germinal vesicle (figs. 64, 65 h) cannot be seen ; for, as the 
erosion of the yolk commences on the surface (fig. 66 c) and gradually passes towards 
the centre, the vesicle is always covered by a layer of opake granules. 
As the solution of the yolk goes on, the opake granular mass in the centre be- 
comes less and less, leaving a clear margin of fluid surrounding it on all sides 
(fig. 66 c). Some granules, however, escape, and are seen floating in the fluid ; but they 
are larger in size, and more transparent than the original yolk-granules (fig. 66 w). 
About this period the ovum acquires another chorion, consisting generally of two 
membranes, and becomes more elliptical in form. 
The three membranes that surround the ovum at this period, as they are all formed 
in the same way, and are exactly alike, may be considered as three layers of the 
same chorion (fig. 66 f), secreted at different times by the oviduct. 
When the granular mass has been much reduced in size (fig. 66 c) it suddenly 
loses its opacity ; and thus the whole vitellus is transformed into a few large, nearly 
transparent granules (fig. 67 w), among which we look in vain for a germinal vesicle ; 
and only now and then are we able to distinguish one granule to be a little larger 
than its fellows (fig. 67 a), and to contain within it a dark spot (fig, 67 Jc). 
In short, the germinal vesicle (figs. 64 to 66 b) ruptures, when disintegration has 
gone on to a certain length, and its disappearance is immediately followed by the 
transformation of the remaining vitelline granules. 
I propose to call these transformed or altered granules by the name of embryonic 
granules (figs. 67, 68 n), since they appear about the same time as the embryonic 
vesicle, and with it assist in forming the embryo. 
After the rupture of the germinal vesicle (figs. 64,65 b), the interior of the egg is 
filled with the embryonic granules (fig. 67 n), not, however, packed close like the 
vitelline, but floating loose. About the centre of these granules, one a little larger 
than the rest (fig. 67 a) may sometimes be seen, having within it an opake spot 
(fig. 67 b). On comparing these with the nucleus and nucleolus of the germinal 
vesicle (fig. 64 a, k) before its rupture (fig*. 64 b), I found them to resemble each 
other completely, having the same size, shape, and appearance, the same degree of 
refraction, and the same position. 
The germinal vesicle immediately before its rupture (figs. 64, 65 b) is r^ooth of an 
