increased in height and are now nearly cuboldal. The por- 

 tion, where it is s-^rollen out into a vesicle, becomes drawn 

 away 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 ei trier 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 ecto- 

 dermal evagination, and grov/s out into the latter, but the 

 thin walls below nov; come together, and close off tne upper 

 portion as a thick-walled vesicle, without, however, severing 

 the connection. This process is readily understood from 

 Pig. 8, in which the walls of the lower part of the partition 

 have become united again. 



In Pig. 1, a bud is shown at tnis stage from the 

 exterior. 



As the ectoderm continues to push out, it becomes 

 constricted where it passes over into the stolonic ectoderm, 

 the constriction being greater at first before and behind 

 than on the sides. The bud-rudiment, which by this time is 

 almost spherical, is sharply marked off from the stolon, and 

 stands eitner straight out as a round knob from the surface 



• 10- 



