404 LEFEVRE. [Von. XIV. 
cation foratime. In Fig. 32, c, the division of the originally 
simple sphere is seen, but the section is not in the proper 
plane to show the connection between the two cavities. 
One of these lobes gives rise to the testis, the other to the 
ovary, according to Van Beneden and Julin, who have described 
‘in detail how, from the primitive, simple sphere and the single 
cord of cells, testis, ovary, vas deferens, and oviduct are all 
differentiated. 
My observations would, therefore, seem to support the view 
of the Belgian authors that the male and female sexual organs 
do not arise from separate vesicles, as described by Kowalewsky 
(12) in the buds of Perophora, but are formed from one and the 
same rudiment. 
Summary of Results. 
(1) The rudiment of the Perophora bud, like that of all other 
ascidians, consists of two vesicles, an outer and an inner one. 
The former is derived from the ectoderm of the stolon, the 
latter from the thickened evaginated wall of the stolonic 
partition. 
(2) At an early stage the right side of the inner vesicle is 
found to be much thicker than the remaining portion, and, by a 
peculiar process of rotatory growth or displacement of the 
vesicle, is carried down to the ventral side of the bud, where it 
forms the floor of the pharynx. This process seems to be due 
to the growth and flattening out of the cells composing the 
whole wall of the vesicle, except in the thickened region. I am 
at a loss to explain why the displacement of the vesicle should 
occur, and to discover the phylogenetic significance of it, if it 
have any. 
(3) The peribranchial sacs arise asymmetrically. As the 
displacement proceeds, the wall of the inner vesicle is folded 
in at the point where the right side of the vesicle joins the 
stolonic partition to form the /eft peribranchial sac. The con- 
nection of the latter with the partition of the stolon is retained 
until a much later stage. A longitudinal furrow appearing high 
up on the right side of the inner vesicle separates off the right 
