Budding in Perophora. — 221 
the middle of the thickened portion of the inner vesicle. 
From its position on the right side it is moved down to the 
ventral mid-line by the*rotation of the vesicle. 
6. The common rudiment of the dorsal tube and nerve- 
ganglion arises as a solid string of mesenchyme-cells, which 
are closely applied to the outer surface of the inner vesicle a 
little to the deft of the median dorsal line. The cord acquires 
a lumen, which later communicates with the pharynx. When 
the rotation is completed the dorsal tube lies in its definitive 
position in the median line. The nerve-ganglion is con- 
stricted off from the dorsal wall of the tube. 
BoOTRYLLUS. 
In the latter part of the summer of 1894 I was given an 
opportunity, through the kindness of Col. Marshall MacDonald, 
the Commissioner, to work in the laboratory of the U.S. Fish 
Commission at Woods Holl, Mass. While there I collected 
material for the study of the bud-development of a species of 
Botryllus—B, Gouldii, Verrill—which was found in great 
abundance. 
The results of my work on this Ascidian show such a com- 
plete agreement with Hjort’s description of the bud-develop- 
ment of this genus that scarcely a word need be added. ‘The 
inner vesicle of the bud is derived from the wall of the peri- 
branchial sac in both larvee and buds, and gives rise to all the 
important organs. As the peribranchial sacs in the larva are 
derived from the ectoderm, it follows that all the important 
organs of the bud are ultimately of ectodermal origin. 
The peribranchial sacs are formed, as Hjort states, by two 
parallel ventral infoldings, which cut off from the inner 
vesicle a saddle-shaped bag surrounding the median vesicle 
dorsally and laterally. The dorsal portion connecting the 
lateral sacs is not formed by a fusion of the latter, but is 
present from the beginning. The dorsal tube is formed as an 
anteriorly directed diverticulum of the dorsal wall of the inner 
vesicle in the region which becomes the median portion of the 
peribranchial cavity. The tube secondarily acquires an 
opening into the pharynx before the communication with the 
peribranchial cavity is lost. 
I might also state that my sections entirely confirm Hjort’s 
description of the formation of the ganglion, and directly 
contradict Pizon’s statement* that. the constriction of the 
ganglion from the dorsal tube cannot be established. 
* Ann. Sciences Nat. 1892 and 1893. 
Ann. & Mag. N. Hist. Ser. 6. Vol. xvi. 16 
