6 Desor on the Embryology of Nemertes. 
flask, (fig. 14,) I saw the yolk granules escape from one of the 
divisions, leaving untouched the clear spot, which now appear- 
ed as a well-defined drop, (a). At the same time, one of the 
three yolks broke, and I saw that the divisions, which till then ` 
were angular, assumed ovoid or spherical forms, (b.) 
On the sixth day I found the divisions much farther ad- 
vanced, and the yolks assuming the mulberry form, as shown 
in fig. 15. The yolks were still crowded together, especially 
in those flasks containing many yolks. 
On the succeeding days, the subdivisions continued to pro- 
gress, so that the yolks appeared to consist of small granules, 
fig. 16 representing a flask on the ninth day. A remarkable 
point about this flask was, that whilst the two upper yolks 
were exceedingly subdivided, the lower one, (d), was almost 
homogeneous, with a single large transparent spot, and had 
merely commenced its subdivision, showing that it had been 
. arrested in its development. The simultaneous existence of 
this undivided yolk, having a single large clear spot, with two 
other yolks much subdivided, and having no single large spots 
but only the small ones in each granule, induced me at first to 
believe, that the small clear spots owed their origin to the 
subdivision of the large one, as is generally supposed ; but 
having seen in other specimens the simultaneous existence 
of both kinds, (fig. 15,) I was convinced that this idea was 
not correct as applied to the Nemertes, and that there must 
be an increase of the transparent liquid during the devel- 
opment. : 
On applying pressure to the flask of fig. 16, the upper 
yolk burst, and I saw the granules escaping in the form of 
little spheroids, each having its clear spot, which appeared to 
occupy one-fourth, and sometimes one-third, of its bulk, (b.) 
The granules were now surrounded. each by its own mem- 
so that on the death of the egg the yolk decomposed 
into as many spheres as there are divisions, 
It is not uncommon for small parts of the vitellus to sepa- 
rate from the mass, during the course of the development, 
