202 Y § 6 bal GI PNG [VoL. XII. 
it is at its posterior middle part, so that later it becomes 
a posteriorly extended portion of the branchial sac; compare 
Figs. 62, 63, and 64, in which 67s’. indicates the portion of 
the vesicle referred to. But it must be noticed that this is 
nothing more than the somewhat narrowed rear end of the 
branchial sac leading to the oesophagus (0e., Fig. 62), and ex- 
tends back only a very short distance behind its opening. 
Fig. 64 represents a section only three sections, 7%p 
thick, farther back than the one shown in Fig. 62, passing 
through the opening of the oesophagus; and in this it will 
be noticed that the cavity 67s’. does not appear, though the 
stomach does. This is practically the condition found in the 
adult zooids. However, the fact that this coecum, as it may 
be called, is the vestibule to the oesophagus need not, in view 
of its relations to the branchial sac and pericardium, stand 
seriously in the way of regarding it as representing the 
epicardium. But to make it correspond with this structure 
in Clavelina, its relation to the septum would require such 
a radical transformation of things as makes it very difficult to 
believe that the two structures are genetically related to each 
other. To shift the connection of the septum from the ferv- 
branchial sac on the /eft stde of the body, to the pericardium on 
the zzght stde, would be a rather serious matter, it seems to me. 
Having thus shown a radical difference between Clavelina 
and Perophora in the relations of the pericardium to the stolonic 
septum, and of the septum to the branchial apparatus, I leave 
the subject for the present to resume it again later on from a 
more general point of view. 
4. THE HyYpopHysIS AND GANGLION. 
It was pointed out in my preliminary communication that 
while in both Goodsiria and Perophora the investigation of 
this subject encounters special difficulties, it fortunately hap- 
pens that the difficulty is not at the same point in the two 
genera. 
In Goodsiria, as we have seen, the origin of the common 
Anlage of duct and ganglion from the zuner vesicle is observed 
