664 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Gastrulation in Chelonia.* — Prof. K. Mitsukuri finds from a study 
of embryos of Chelonia caouana , Trionyx japonicus and Clemmys japonica, 
that when segmentation has gone on for some time two layers are estab- 
lished in the blastoderm, the epiblast is composed of columnar cells, and 
the lower layer of irregular stellate cells, which probably do not form a 
complete sheet. This separation into two layers takes place in all parts 
of the blastoderm, except a small area at the posterior end of the future 
embryo, where there is a thick knob formed of a network of cells ; this is 
the primitive plate or knob. 
In the middle of this knob an invagination cavity at first goes 
straight downwards, but soon takes a forward horizontal course. This 
is the archenteron, with the blastopore ; the roof of the cavity becomes 
continuous with the epiblast of the embryonic shield and becomes 
columnar; out of the median part is formed the notochord, and from 
columnar epithelium on each side there is developed the gastral meso- 
blast. The floor of the cavity gives rise, posteriorly, to the peristomial 
mesoblast, while the anterior part is absorbed, and the invagination 
cavity is thus put into communication with the large subgerminal cavity 
in the yolk. The primitive knob grows forwards, and its advance in 
later stages is marked by a zone of cell-network with a compact central 
area. When the whole of the ventral surface of the embryonic shield 
has been covered the process stops, and the cell-network is changed 
into compact cellular sheets. The future embryo, and consequently the 
definite alimentary canal, is formed entirely within the area which is 
covered ventral] y by the part derived from the primitive knob. 
Or the results may be put thus. From the epiblast of the embryonic 
shield the epiblast and its derivates are derived. In the region of the 
primitive plate and its anterior enlargement are produced the invagination 
cavity (archenteron), the yolk-plug, the notochord, the mesoblast, and the 
definite hypoblast with its derivatives. The primitive lower layer con- 
tributes to the future animal only in so far as some of its cells are unre- 
cognizably incorporated with the cells of the primitive knob, when the 
latter spreads itself over the ventral surface of the embryonic shield. 
Of points which the author desires specially to emphasize we may 
note — 
(1) The primitive plate or knob is raw material left at the centre of 
the blastoderm, by means of which certain palingenetic processes are 
gone through. 
(2) The yolk-sac must be regarded as a ventral appendage of the 
archenteron in which nutrient matter is stored, but 
(3) Owing to the enormous size of this sac it and the archenteron 
are formed separately from one another, and come only secondarily into 
contact, jy 
Development of Bulbus Cordis in Amphibians and Reptiles.f — 
Dr. A. Danger has studied this in frog, salamander, and lizard, in order 
to discover what relation there is between the conus of Amphibians and 
the bulbus of Birds and Reptiles. The arterial valves of the lizard 
* Joum. Coll. Sci. Imp. Univ. Japan, vi. (1894) pp. 227-77 (3 pis. and 8 figs.). 
See this Journal, 1893, ^p. 007. 
f Morphol. Jahrb., xxi. (1894) pp. 40-67 (22 figs.). 
