176 RITTER. PVor. Shi. 
d. The Hypophysis and Ganglion. 
a The Ganglio-hypophyseal Duct.— The hypophysis always 
arises very early, in some buds its origin being the first inter- 
ruption of the simple spherical form of the primitive inner 
vesicle. This is the case, for example, in the bud a section of 
which is represented in Fig. 43, Pl. XV. Its method of origin 
can be very well seen by examining with a low magnify- 
ing power a whole bud from its dorsal side, the bud having 
been first cleared in oil. A drawing of such a bud is shown in 
Fig. 16, Pl. XIII, where Zy.a. is the Anlage of the organ now 
under consideration. By observing it under a constantly 
changing focus, one finds that it is a groove-like evagination 
from the dorsal wall of the inner vesicle. A transverse section 
of a bud in the same stage of development, and cutting the 
evagination, is presented in Fig. 43. The groove is very simple 
and is quite uniform throughout its length. 
The same section is shown at éd., in Fig. 5, Pl. XII, where the 
clearly seen orientation of the bud in the colony, and the posi- 
tion of the evagination on the dorsal side of the bud, leave no 
room for doubt that the evagination is the beginning of the 
hypophysis. The Az/age remains in this groove-like condition 
only a short time ; for in a stage of development of the bud 
only a little more advanced than that shown in the two figures 
to which attention has just been directed, it appears as a tube 
wholly separated from the vesicle, except at its anterior end, 
where its lumen communicates with the cavity of the vesicle. 
This communication remains throughout the life of the animal 
as the mouth of the hypophysis. As the tube becomes con- 
stricted off from the wall of the vesicle, it terminates posteriorly 
as a simple blind pouch, and does not at any stage communi- 
cate with either of the peribranchial sacs, as is agreed by Oka, 
Hjort, and Pizon to be the case in Botryllus. Hjort (95) also 
shows such a communication in Glossophorum sabulosum. But 
as remarked by Hjort and Bonnevie ('95), p. 392, this commu- 
nication can have very little significance. They base this 
remark on the fact that it does not take place in the buds of 
Distaplia magnilarva, studied by them, while it does in the 

