No. 3.] BUDDING IN PEROPHORA. 373 
The first indication of the appearance of a bud is a slight 
bulging out of the ectoderm of the stolon at one point, and if 
a transverse section be taken at this spot, it will be seen that 
the two layers of the partition have spread widely apart, giving 
the appearance of a more or less spherical vesicle in section. 
This is well shown in Pl. XXX, Fig. 7. The walls of the par- 
tition are seen to be no longer composed of flat cells, except on 
the lower side, that is, the side next the surface of attachment, 
but have become very much thickened by active cell multiplica- 
tion. The cells, too, of the ectoderm over the thickened portion 
of the partition have increased in height and are now nearly 
cuboidal. The partition, where it is swollen out into a vesicle, 
becomes drawn away at its lower border from the outer wall of 
the stolon; I do not think that this is due to shrinkage, for it 
is invariably found, and, moreover, beyond this region on either 
side, where the partition is still flat, it is seen to stretch clear 
across the lumen of the stolon. 
The ectoderm continues to bulge out more and more, until it 
forms a hemispherical protuberance on the surface of the 
stolon. The cells composing the raised portion of the ectoderm 
do not remain cuboidal, but from now on, as the swelling 
increases, become gradually flattened again. The thickened 
portion of the partition keeps pace with the ectodermal evagi- 
nation, and grows out into the latter; but the thin walls below 
now come together, and close off the upper portion as a thick- 
walled vesicle, without, however, severing the connection. This 
process is readily understood from Pl. XXX, Fig. 8, in which 
the walls of the lower part of the partition (/z.), have become 
united again. 
In Pl. XXIX, Fig. 1, a bud at about this stage is shown from 
the exterior. 
As the ectoderm continues to push out, it becomes con- 
stricted where it passes over into the stolonic ectoderm, the 
constriction being greater at first before and behind «han on 
the sides. The bud-rudiment, which by this time is almost 
spherical, is sharply marked off from the stolon, and stands 
either straight out as a round knob from the surface of the 
latter or is slightly inclined towards its free tip (Fig. 2). 
