10 Desor on the Embryology of Nemertes. 
of different sizes, but all spherical and nucleolated. The mar- 
gin of this part only is bordered with angular epithelial cells, 
to which are attached the cilix. Inside of this is another large ` 
mass of cells, (0), similar to those of the outside, being with- 
out doubt the residue of the vitellus destined for the support 
of the animal. When isolated, (z), they are spherical, and 
contain likewise a clear spot, which nevertheless is less dis- 
tinct than in the cells of the outer coat, and is sometimes com- 
pletely wanting. 
As soon as the animal leaves its envelop, it moves with 
‘great ease in all directions, bending and contracting itself as 
it pleases. When elongated, (fig. 22 a), there is seen, as we 
have already stated, a longitudinal clear stripe, extending 
upwards from the inside yolk, (c). If the animal contracts 
itself, (fig. 24), this stripe becomes so much shorter as to ap- 
pear transverse instead of longitudinal. This fact convinced 
me at once that this stripe was nothing more nor less than the 
crescent-like spot, formerly spoken of, in an elongated state, 
being the first appearance of the alimentary canal. 
'The animal moves with as much ease when taken out of the 
flask and placed in water as before, showing that the change 
of medium has no effect upon it. It appears perfectly mas- 
ter of its movements, and on seeing it swimming about, and 
striking against different objects, one might suppose it endow- 
ed with a certain amount of curiosity. Sometimes, also, 1 
saw them shake themselves convulsively, as if they had a 
chill. 
Commonly, the embryo does not leave the flask imme- 
diately after having freed itself from the envelop; on the con- 
trary, it remains there sometimes for days. The changes 
which now take place, on about the thirtieth day, concern 
principally the internal parts. The residue of the yolk not 
only diminishes in volume, but becomes less and less opaque ; 
the intestine likewise becomes more distinct ; it assumes now 
the appearance of a proper tube, which extends from the 
vitellus to the upper part of the body, and is seen even to 
