608 
8UMMARY OF CURRENT RESEARCHES RELATING TO 
and its dorsal opening is the blastopore. This cavity extends gradually 
forwards as the primitive knob enlarges anteriorly. The roof of the 
archenteron, which becomes continuous with the epiblast at the dorsal 
lip of the blastopore, becomes columnar ; and from the median part of 
the roof the notochord and gastric mesoblast are formed. On the floor 
of the archenteron becoming divided into two parts the larger and 
posterior portion gives rise to the peristomial mesoblast, while the rest 
is finally absorbed, together with that part of the primitive knob which 
lies beneath it ; the archenteron is thus put into communication with 
the large subgerminal cavity in the yolk. The primitive knob continues 
to spread till the whole of the ventral surface of the embryonic shield 
has been covered. At some distance back from the anterior end of the 
embryonic shield the head-fold is developed. As the primitive knob 
marks the posterior end of the embryo, and the lateral folds arise 
within the embryonic shield, it would appear that the future embryo- 
body is developed entirely within the area covered ventrally by the 
part derived from the primitive knob. 
In other words, the epiblast of the embryonic shield gives rise to the 
epiblast and its derivates ; in the region of the primitive plate and its 
anterior enlargement there are produced the archenteron, the yolk-plug, 
the notochord, the mesoblast, the definite hypoblast and its derivates. 
The only contribution to the body of the embryo made by the primitive 
lower layer is to be found in some of its cells which are mixed up with 
the cells of the primitive knob. 
Looking at the matter generally, the author is led to the view that 
the enclosure of the yolk of the. Chelonian egg is a simple growth of the 
edge of the blastoderm, and is cenogenetic in nature, while in Elasmo- 
branchs it is a part of the process of invagination, and is palingenetic. 
He rejects, therefore, Balfour’s theory of a yolk-blastopore in Sauropsida. 
Life-history of Rhodens amarus.* — Dr. Ad. Olt describes the 
peculiar metamorphosis of the embryos of this Cyprinoid Fish during 
their stay in the gills of mussels, the remarkable structure of the 
sexually mature female, and the system of currents within the bivalve. 
The Bitterling is widely distributed in Central Europe. It spawns 
from the middle of May to the middle of July, laying its eggs within 
species of TJnio and Anodonta. An ovipositor is inserted at the exhalant 
aperture, and the ova pass into the interlamellar spaces of the gills. The 
nature of the ova and the mode of their transmission are described in 
detail. Milt is shed by the males near the respiratory siphon. While 
the ova enter against the stream, as above noted, the spermatozoa follow 
the currents. 
After a few notes on the segmentation of the ovum, Dr. Olt describes 
the embryos. Very remarkable is the manner in which the yolk serves 
as an attaching and protective organ. The precise relations of the 
embryos to the gills are noted. 
The females are remarkable in having an ovipositor and an accessory 
gland. The ovary is single, but was originally paired. In the posterior 
part of the body-cavity, covered by peritoneum, lies the paired accessory 
gland with a common duct, which may be regarded as the beginning of 
* Zeitschr. f. wiss. Zool., Iv. (1893) pp. 543-75 (1 pi.). 
