774 SUMMARY OF CURRENT RESEARCHES RELATING TO 
the Botryllidae differs so far from that of other Ascidians, such as 
Perophora, Didemnium , or Distaplia , that the inner vesicle is always, 
directly or indirectly, formed from the endoderm. The intestinal tract, 
the peribranchial vesicle, and the nervous system are given off from this 
inner vesicle. 
The process by which the peribranchial vesicle is formed begins 
with the formation from the ventral wall of the internal vesicle of folds 
which project into its interior; a median vesicle is thus formed, which 
communicates by two orifices with the two lateral peribranchial vesicles. 
The first rudiment of the nervous system is a hemispherical evagination 
which appears at about the middle of the dorsal wall of the median 
vesicle. A tube which opens by both ends into the median vesicle 
soon appears, and this becomes thickened on its ventral side ; it becomes 
mor^and more cut off from the dorsal portion of the tube, and fine fibres 
are formed in its interior. The thickening becomes the permanent 
ganglion, while the tube, which gets longer and thinner, persists as the 
hypophysis. The author’s results are by no means in accordance with 
those of Seeliger or Salensky. 
In the study of compound Ascidians, Dr. Hjort has discovered 
several points of agreement between gemmation and larval develop- 
ment. In the cerebral vesicle of Distaplia magnilarva there is, at an 
early stage, a difference between the left and right sides. From the 
right there arises an outgrowth which soon exhibits the most various 
differentiations, and from which the larval brain arises ; the left side 
continues to retain the indifferent character of its cells. The anterior 
part of the brain-vesicle becomes fused with the enteron, and later, 
becomes perforated and so forms, during the whole of the larval period, 
a communication between the enteron and the brain-vesicle. The 
multilaminate left wall of the vesicle becomes thickened at about its 
middle to form the permanent ganglion, and this thickening is more 
and more constricted off. The left wall elongates and represents the 
so-called ciliated pit. While the larval brain, which is formed by 
evagination from the right wall of the cerebral vesicle, is being con- 
stricted off, the epithelioid left wall of the primitive brain-vesicle 
forms a tube which is a direct continuation of the ciliated pit, and 
is regarded as the hypophysis. 
We find, therefore, that in both larval development and gemmation 
the hypophysis and the persistent’ ganglion have a common origin ; 
this is, in both modes of development, tubular, and in both cases the 
ganglion is formed as a thickening of the tube. The larval brain- 
cavity opens, as Kowalevsky asserts and van Beneden and Julin deny, 
by the hypophysis into the enteron. In the adult developed from the 
larva the lumen of the hypophysis is the only part of the lumen of the 
larval brain-vesicle which is persistent. 
Development of Hypophysis in Ascidians.* — Mr. A. Willey, who 
has come to similar results as Dr. J. Hjort (see supra') with regard to the 
development of the hypophysis in Ascidians, has a preliminary notice of 
his researches. He has worked with Ciona intestinalis and Clavelina 
lepadiformis. He supports Kowalevsky, as against Van Beneden and 
* Zool. Anzeig., xv. (1892) pp. 332-4 (1 fig.). 
