No. 3.] BUDDING IN PEROPHORA. 4OI 
Mesodermzellen bilden sollte, scheint mir so gering zu sein, wie 
fiir die Auffassung Herdman’s, dass die innere Blase der 
Knospenanlage einen solchen Ursprung habe.” 
About the time that the peribranchial cavity is completely 
cut off from the inner vesicle, the anterior extremity of the 
dorsal tube fuses with the dorsal wall of the branchial sac, an 
opening breaks through, and the lumen of the tube is put into 
communication with the branchial cavity. The posterior end 
of the tube abuts against the anterior wall of the cloaca, but 
never opens into the latter, in contrast with the condition 
found in Botryllus and many other ascidians. 
Pl. XXX, Fig. 14, represents a median sagittal section of a 
bud before the complete separation of the peribranchial cavity, 
and, therefore, before the dorsal tube has acquired an opening 
into the branchial sac. The section passes through the entire 
length of the tube (d.7.), which is seen to be closed at both 
ends and made up of an epithelium of one layer. 
In my preliminary work on the budding of Perophora, already 
referred to, I made the statement that “the ganglion is formed 
by a thickening of the dorsa/ wall of the tube, which eventually 
becomes constricted off in the manner described by Hjort for 
Botryllus, although in the latter it is the ventral wall of the 
tube which gives rise to the ganglion.”” More careful study of 
very young stages, however, has convinced me that the above 
is not an accurate description of the formation of the ganglion. 
After the communication between the dorsal tube and 
branchial sac has been established, a few cells, identical in 
appearance with the amoeboid blood cells, are found adhering 
to the dorsal surface of the tube throughout the greater part of 
its length; this elongated, loose patch of cells constitutes the 
rudiment of the ganglion (Pl. XXXII, Fig. 27, a, gir). 
It is a difficult question to decide whether these cells are 
entirely cells of the blood, as their appearance indicates, or 
whether they are derived by proliferation in the wall of the 
tube, for in many places the boundary line of the latter is 
broken, and there is no sharp demarcation between the cells of 
the rudiment and those of the tube, as seen in Big, 270 
Many sections, however, such as the one shown in Fig. 27, 3, 
