No: 3.) BUDDING IN PEROPHORA. 405 
peribranchial sac, and is gradually borne ventrally, as the 
shifting of the vesicle continues. The constriction of the 
whole peribranchial cavity eventually takes place in such a way 
as to cut off from the peribranchial sac a saddle-shaped bag, 
composed of the median dorsal connecting piece or cloaca and 
the two lateral portions of the cavity. Anterior and posterior 
extensions of the latter grow out and surround respectively the 
anterior and posterior ends of the pharynx. The posterior 
prolongations are possibly to be regarded as homologous with 
the epicardial sacs of some other ascidians. 
(4) The endostyle appears early as a longitudinal groove in 
the middle of the thickened portion of the vesicle; from its 
primitive position on the right side it is moved down to the 
ventral mid-line by the displacement of the vesicle. 
(5) The digestive tract grows out laterally as a blind tube 
from the posterior end of the inner vesicle high up on the left 
side. During the change in position of the vesicle its opening 
into the latter is carried up into the median plane. 
The “organe réfringent”’ arises as a tubular diverticulum 
from the anterior face of the stomach, and produces a dichoto- 
mously branched system of tubules, which surround the intes- 
tine and terminate in little dilated vesicles or ampullae. 
(6) All the evidence goes to show that the pericardium is 
formed from free amoeboid cells of the blood. It first appears 
as a clump of cells adhering to the outer surface of the inner 
vesicle far up on the right side, and through the shifting of the 
vesicle is brought down to the ventral side. 
(7) The dorsal tube and ganglion are formed only in part 
from a common rudiment, but there is every reason to believe 
that both are derived solely from cells of the blood. The 
former appears as an elongated, solid mass of cells, which lies 
close against the outer surface of the inner vesicle, a little to 
the left of the median dorsal line. When the displacement of 
the vesicle is completed, the rudiment lies in the median plane; 
it then acquires a lumen, which is put into communication 
anteriorly with the cavity of the pharynx. The ganglion has a 
double origin, and is formed by proliferation of the upper wall 
of the dorsal tube and also by addition of cells of the blood. 
