164 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
above. Soon this also goes, separates from the embryo, and forms at its 
sides the enveloping fold ( Faltenhulle ) seen in other Salpee. 
The inner mesenchyme mass divides the histogens into two groups 
in which two clefts appear. These unite as the branchial cavity. From 
the base of this the gill is constricted off. The cloaca is simply a part 
of the branchial cavity. The heart is a constriction, the gut an out- 
growth, of the same cavity ; but all the other organs arise from histogens 
without relation to ectoderm or endoderm. 
In another investigation * Korotneff has studied in detail the stolon 
of Salpse. Besides the genital strand, the nerve-strand, and the two 
cloacal tubes, described by Kowalevsky, the author discovers a fifth or 
pericardial strand. To an account of this a chapter is devoted. 
The author then describes tbe extraordinary phagocytosis in the 
elseoblast, placenta, and “ blood-bud ” ( Blut-lmospe ) of Salpa pinnata. 
Where the “ Zellenkampf ” is keenest, he finds colossal cells, whose pos- 
sible function is suggested in the title “ nephrocytes.” These are of 
course in addition to the five kinds of free cells which Salensky has dis- 
tinguished, and they add a new complication. 
What the author has to say in regard to the relation of blastomeres 
and kalimmocytes has been already referred to. As to the difficult 
question of metagenesis, his opinion is as follows : — 
There is a reproductive division of labour, one generation simply 
producing germ-cells, the other nursing. “ The germ-cells arise exclu- 
sively in the first generation, which may be therefore called the germ- 
producer or Gonogen ; the second generation forms no germ-plasm, but 
is merely a nurse, and may be called the brood-animal or Gonotroph .” 
Development of Diplosoma Listeri.j — Prof. W. Salensky makes 
another detailed contribution to the embryology of the Synascidians. 
The ovum has three concentric envelopes, — an external cellulose 
sheath, an ectoderm sheath, and a follicular layer. In the regular total 
segmentation, the bilateral symmetry which E. van Beneden and Julin 
demonstrated is very clearly illustrated. As to the bilateral develop- 
ment of the nerve-cord, nothing was observed ; it appeared as an axial 
thickening of ectoderm after the closure of the blastopore. The primi- 
tive mesoblasts, however, show thorough symmetry. 
Salensky describes the organogenesis in detail, — the closure of the 
medullary groove (with an explanation of the Dachzelle) ; the differen- 
tiation of endoderm from the common meso-endoderm ; the origin of 
somatic mesenchyme and caudal muscle-plates from one and the same 
rudiment ; the development of the peribranchial sacs ; the formation of 
the cellulose mantle from the kalimmocytes exclusively (though in 
post-embryonic stages the mesenchyme may share), and the final de- 
velopment of the twin individuals. 
Theory of Ascidian Buds.J — Dr. J. Hjort returns to the difficulty 
raised by what he believes to be a fact — that in Botryllid-buds, the ner- 
vous system, gut, and peribranchial sac all arise from a common vesicular 
rudiment, which in turn is formed by an evagination of the peribranchial 
sac of the parental organism (whether larva or bud). Thus the young 
* MT. Zool. Stat. Neapel, xi. (1894) pp. 325-67 (3 pis., 9 figs.), 
f Tom. cit., pp. 368-474 (4 pis., 1 fig.), 
j Anat. Anzeig., x. (1894) pp. 215-29 (5 figs.). 
