24 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
there multiply asexually, and gradually ascend to the surface. He has 
been able to work out the life-history with some degree of completeness. 
I. The formation of the stolo prolifer. The posterior ventral end 
of a young Pyrosoma from an older colony shows three distinct portions 
which form the bud-generation. There is an ectodermic portion, an 
endodermic tube or process of the endostyle, and a mesodermic germinal 
strand, along with a number of mesenchyme cells. In an early stage, 
the author describes the thickening of the ectoderm, and the origin of 
the peribranchial tubes from the mesoderm. A further step involves 
the ditferentiation of the endodermic tube, and of the mesodermic masses 
filling the cavity of the stolon. In connection witli the mesodermic 
strand, the peribranchial tubes, the reproductive strand, liberated mesen- 
chyme cells, and the neural canal are described. Seeliger shows the 
essential agreement between Pyrosoma and Salpa, as regards the forma- 
tion of buds, and contrasts this with the very variable processes in 
other Tunicates. He has previously maintained the phylogenetic inde- 
pendence of the process in the two series. 
II. The modification of the stolo 'prolifer into the Pyrosoma chain. 
The stolon grows in length, and divides into distinct regions. In a 
chain of four or five thus formed, the individuals are still in com- 
munication through their pharyngeal and (primary) body-cavities, but 
as in Salpse the connection is readily broken. The plane of the stolon 
marked by the primary neural canal and the genital strand corresponds 
to the median plane of the adult animals. The neural-haemal axis of 
each stolon-segment corresponds to the subsequent longitudinal axis, 
while the longitudinal axis of the stolon and its several segments is the 
future dorso-ventral axis. This is the result of a marked inequality of 
growth and consequent displacement in the segments. The ectoderm 
is of least importance in the differentiation ; it produces the cellulose 
tunic, is pierced by the inhalant and exhalant apertures, and forms long 
tubular outgrowths which j^enetrate the mantle as blood-courses. The 
endoderm divides very early into a proximal and a distal portion, of 
which the first remains for a while without any essential change, but the 
second developes into the pharynx and digestive canal of the Pyrosoma. 
This change is described at length. The discussion of the mesoderm 
begins with an account of the peribranchial tubes. These are at first 
continuous along the whole of the young stolon, but soon divide into 
segments corresponding to the buds. They grow especially towards the 
hmmal surface where their median margins meet below the intestine, 
and are obliterated to form the cloaca. The appearance of the gill-slits 
and their relation to the peribranchial chamber are then noticed. The 
history of the primary neural canal is traced. The persistent ganglion 
appears far forward on the original neural vesicle from which it soon 
becomes distinct. The ciliated groove, a sac-like expansion homologous 
with the “ hypophysis-gland ” of Ascidians, the first hints of an eye, 
the disposition of the nerve-strands are discussed in order. Seeliger 
compares the development of the central nervous system with the very 
similar j)i*ocess in Pyrosoma, and with the development of the true 
embryos. Some of the free mesoderm cells form blood, while others 
are fixed as true connective-tissue elements, and form a homogeneous 
matrix which in old animals fills up the primary body-cavity. Further- 
