No. 3.] BUDDING IN PEROPHORA. 371 
origin in the ascidian larva has been a question of much dis- 
pute. Kowalewsky (11) first showed that in the larva of simple 
ascidians the peribranchial sacs are formed as two symmetri- 
cal ectodermal invaginations, which later fuse together dorsally 
and surround the branchial sac. Della Valle (4), however, 
contradicted these results, and maintained an endodermal origin 
for the peribranchial sacs in both simple and compound ascid- 
ians, and Pizon (22) has recently described the sacs as arising 
from two diverticula from the branchial sac in the larva of 
Botryllus. _Kowalewsky’s account is borne out by all the later 
investigation of the subject, with the exception of that of 
Pizon. Seeliger (29, Clavelina), Willey (36, Ciona), Salensky 
(28, Diplosoma, Didemnum), and Caullery (1, Distaplia, Lepto- 
clinum, Glossophorum, Circinalium) agree in their statements 
that the peribranchial sacs arise in the manner described by 
Kowalewsky, and are therefore purely ectodermal. It is fairly 
safe to assume that Pizon is wrong, and that in Botryllus, as in all 
other ascidians studied, the sacs are ectodermal. If this be the 
case, as the inner vesicle of the bud-rudiment is directly cut off 
from the outer peribranchial wall in both embryozodid and blasto- 
zooid, it follows thatall the organs,including the peribranchial sacs, 
derived from this inner vesicle throughout the entire series of buds 
proceeding from the larva are ultimately of ectodermal origin. 
After this brief review of the state of our knowledge con- 
cerning the origin of the bud-rudiment in the ascidians, I shall 
now describe the process as I have found it to occur in 
Perophora viridis. 
The buds arise in a single row along the course of the deli- 
cate stolons, which branch profusely and adhere on one side to 
the surface over which they creep. The branches come off 
approximately at right angles to the stems from which they 
proceed; but aside from this characteristic there is no regu- 
larity whatever in the method of branching —they arise at 
unequal intervals, and as each grows out it gives off in its turn 
still younger shoots, the whole system becoming much tangled 
and twisted to form a loose felt-work. 
Proceeding towards the growing tips of the stolons, both 
buds and branches are seen to become successively younger. 
