396 LEFEVRE. [Vou. XIV. 
the ectodermal wall. Their description, however, is very 
incomplete and unsatisfactory. 
Our more recent knowledge of the subject is due to the 
researches of Pizon (22), Oka (20), and Hjort (8) on Botryllus, 
of Salensky (27) on Distaplia, and of Caullery (1) on Glosso- 
phorum and Diplosoma. The first three authors, although they 
are in agreement concerning the origin of the dorsal tube, differ 
widely in respect to the derivation of the ganglion. According 
to all three, the dorsal tube in the Botryllus bud arises as 
an anteriorly directed evagination of the _peribranchial 
cavity, ending blindly in front, but freely opening into the 
cavity at its posterior extremity. This tube grows forward, 
and its anterior end fuses with the wall of the branchial 
sac, whose cavity is then put into communication with the 
lumen of the tube, while the posterior connection becomes 
obliterated. The definitive opening of the hypophyseal tube 
is, therefore, secondary. So far we find these authors agreeing, 
but it is quite otherwise when we come to consider the origin 
of the ganglion. 
Pizon maintains that the ganglion of the bud is derived 
directly from a fine nerve string, which grows out from the 
ganglion of the parent bud, or, in the first place, from that of 
the larva into the young bud. His view is not based on actual 
observation, and his arguments, which are far from satisfactory, 
fail to convince. He avers that a constriction of the ganglion 
from the wall of the dorsal tube does not take place, but, on 
the contrary, the figures of Hjort (8, Botryllus) prove fairly 
conclusively that such a constriction does actually occur. 
Hjort’s contention that the ganglion is formed from the thick- 
ened ventral wall of the hypophyseal tube is based on a study 
of an unbroken series of stages and is clearly borne out by his 
figures. In a short note! on the budding of Botryllus, which 
was published recently, I added additional evidence in support 
of Hjort’s view, and reproduced a drawing which showed 
beyond a doubt that the thickened ventral wall of the dorsal 
tube is pinched off to form the ganglion. 
The account given by Oka is entirely different. According 
1 Johns Hopkins University Circulars, No. 119, June, 1895. 
