I9O0 RITTER: VoL. Xi: 
2. RELATION OF THE BUD TO THE STOLON. 
The point to be made in this connection may be briefly 
stated by quoting what I have already said in my preliminary 
paper: ‘When the differentiation of the ‘endoderm’ into the 
branchial and two peribranchial sacs takes place, it does so in 
such a way that the developing blastozooid is connected with 
the double-walled partition of the stolon, not by the dvanchzal 
sac, as has been hitherto supposed, but by the left perzbvanchial 
Sat. 
Figs. 57-64, and 65, 67, and 70, Pl. XVI, will suffice to 
illustrate the facts. Of these Figs. 67 and 68 are from the 
youngest stage. At this time the inner vesicle is still almost 
a perfect sphere, no differentiation of organs having yet begun 
excepting that a mere trace, fc.a., of the heart is present. 
The connection of the inner vesicle to the stolonic septum, 
cl’n., does not show in his section, but it does in the third 
section of the series preceding this. The bud at this time 
does not stand out at a right angle to the stolon, but is 
inclined somewhat toward its tip. The series passes from the , 
posterior, or point of attachment of the bud, toward its ante- 
rior, z.e. toward the tip of the stolon. It is for this reason 
that we find the section of the stolonic septum in several sec- 
tions before we come to its place of attachment to the inner 
vesicle. 
The process by which the vesicle becomes divided up into 
the branchial and two peribranchial chambers differs so little 
from the same process in Goodszria and various other Ascidian 
buds, that I have thought it would be sufficient to pass over 
the various stages excepting those that pertain especially to 
the condition about to be described. It is, however, necessary 
to refer to the account given by Lefevre of the first stages in 
the differentiation of the vesicle. He states that in P. vzrzdis 
the inner vesicle rotates to the right through 90° during the 
initial steps in the formation of the peribranchial sacs. Accord- 
ing to him the heart Ax/age, the first organ to appear, is located 
at the beginning go° farther to the dorsal and left of the 
vesicle than the position that it ultimately occupies in the 
