* 
4 Desor on the Embryology of Nemertes. 
The vitelline substance is not a homogeneous mass, nor sim- 
ply granular, as it appears at first sight ; on the contrary, it 
is composed of an accumulation of cells, which are distinetly 
‘nucleated, as ma’ be shown by a magnifying power of only 
150 diameters, and which is very plain in a power of 400 
(fig. 8.) So long/as the vitellus is entire, the cells being 
pressed against each other, have an angular form ; but as soon 
as the vitellus is broken, they become spherical. . Each cell 
contains, usually, but one nucleus, which also seems to be a 
cell ; at least, it is transparent like the cell itself, (fig. 8.) 
At this epoch of the development, that is to say, before the 
furrowing has began, there is no trace of a membrane to be 
observed around the yolk-spheres. It seems that the natural 
cohesiveness of the vitelline substance is sufficient to maintain 
it in a spherical form. The oily drop in the interior may even 
be forced out without breaking the vitellus. In order to break 
served the nant A flask containing several vitelline masses was placed under 
e compresso o 
tinct. While the vitelline substance was escaping, the dot became isolated, 
(Fig. 8 d), and although I used a high power, (400 diam.) I could not perceive any 
assuming the most varied forms, as shown in Fig. 9 This extraordinary flexi- 
bility, taken in connection with the fact that I could not perceive an investing 
membrane, convinces me that it was a mere drop of oily cohering 
Another vitellus having been crushed more rapidly, I could not dones any large 
vesicle, but in place of it many small clear spots having the same limpid appearance 
without any nucleus, from which I concluded that the large drop had been broken 
into many fragments, as in the case shown by Fig. 6 and 7. 
se experiments I think authorize the chaise that the clear spot is formed 
ot a oe Which assumes a spherical form, in c consequence of its 
M er the impossibility of di 
y of discovering any kind of mem- 
— em i fact that it n be broken into many smaller drops of "em appear- 
ance, without any previous appearance of tit 
thet Filia earls d partitions, seem to me to prove 
il-drop 
It remains for future 
ee to haké out what is aa object gus sigaifiention in the economy of 
