No. 3.] BUDDING IN PEROPHORA. 395 
rohr sich eine Anhaufung von sehr blassen Zellen befindet, 
welche bei weiterer Entwicklung zu verschwinden scheinen.”’ 
Amaroucium is one of those ascidians in which the ganglion lies 
above the hypophyseal tube. 
Ganin (5), who studied the bud development in Didemnum 
and Botryllus, derived the nervous system from a vesicle which 
he described as being cut off from the inner vesicle of the bud 
and converted into a long cylindrical tube lying over the dorsal 
wall of the branchial sac. The ganglion, according to Ganin, 
becomes differentiated from a part of this tube, the remain- 
der of which forms a ciliated organ communicating with the 
branchial cavity. His description is very obscure, however, 
and the only points to be noticed are that the dorsal tube, 
according to this author, is derived from the endodermal vesicle 
and that it gives rise to the ganglion. 
Giard (6) and Della’ Valle (3 and 4), who studied the bud 
development in different species of ascidians, contributed nothing 
of value concerning the nervous system, but both ascribe a 
common origin to the dorsal tube and ganglion. 
The views of -Seeliger (29) are very different from the fore- 
going. According to him, the dorsal tube and ganglion in the 
buds of Clavelina arise from a common rudiment, which is 
derived from mesodermal cells. This belief was not based on 
direct observation, since he did not examine sufficiently young 
stages, but was arrived at through theoretical considerations. 
The great similarity between the individual cells of the nerve- 
rudiment and the free blood cells in the body cavity of the bud 
Seeliger holds is good evidence for the mesodermal origin of 
this structure. He furthermore points out that the cells com- 
posing the ganglion of the larva would be carried off in the 
blood after the disintegration of that organ, and give rise in the 
bud to some of these free cells. The latter would, therefore, 
be “directe Abkémmlinge eines friihere ganglidsen Organs,” 
and it would be but natural for them to resume the function 
which they had once possessed. Van Beneden and Julin (33), 
on the contrary, in their work on the development of the buds 
of Clavelina, state that the nervous system is derived from the 
ectoderm, and first appears as a cord of cells lying close against 
