190 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
enlarge into vesicles, and are separated from one another by proliferating 
vessels and connective-tissue strands. Thus the secretory parts dis- 
charge their secretion separately. It passes by pressure through the 
walls of the follicles into the lymph spaces of the connective tissue. 
Prochorion of the Dog.* — Prof. R. Bonnet describes the blasto- 
dermic vesicle in the dog in its earlier stages, with special reference to 
the so-called “prochorion.” Until it exceeds 11 mm. in length the 
ovum lies surrounded by the oolemma (zona pellucida) — at first wholly, 
afterwards less completely — and by an external gelatinous sheath or 
“ prochorion ” of Hensen. On eggs immersed in water a large number 
of transparent threads are seen floating out from the gelatinous sheath. 
These are merely secretion-threads from the uterine glands, of which 
the prochorion is a product. 
Placenta of Weasel.f — Prof. H. Strahl concludes, from his study of 
the early attachment of the mammalian ovum to the wall of the uterus, 
that the syncytial formations occurring during this process arise from 
modifications of the uterine epithelium. Part of this is used in the 
formation of the placenta, and part is disintegrated into what may serve 
as nutritive material. The author has confirmed these conclusions by 
a study of the placenta of Putorius faro. 
Development of Selachii4 — Prof. C. K. Hoffmann begins by de- 
scribing the process of gastrulation and the rudiments of the two primary 
germinal layers. He finds a large gastrular invagination at the posterior 
end of the blastoderm of Acanthias. It is at first a more or less spherical 
vesicle, readily visible to the naked eye ; but the blastopore becomes a 
long narrow cleft, and the archenteric cavity extends forwards between 
the blastoderm and the yolk. The blastopore closes, and from its fused 
lips arises the embryonic rim which forms the first rudiment of the 
embryo. Many authors have mistaken the primitive archenteric cavity 
for the segmentation cavity. None have distinguished it as the primary 
gastrula cavity. But none of it passes into the embryo ; indeed, of the 
whole blastoderm only the embryonic rim is persistent. A “ secondary 
archenteron ” is subsequently formed. The yolk-sac represents the last 
vestige of the original or archi-gastrula. Prom the appearance of the 
segmentation-cavity on to the time when the embryo proper begins to 
develop, no mitotic divisions are demonstrable in the yolk-nuclei, though 
amitotic divisions occur; but after the establishment of the embryo 
begins there is an abundance of mitotic divisions in the yolk-nuclei, 
which certainly have a direct share in the development of the germinal 
layers and embryo. 
The bilateral mesoderm and the notochord arise from the embryonic 
rim ( TJrmund ) ; the gastral or axial mesoblast seems to arise as a paired 
outgrowth from the archenteric wall. 
The protovertebrse of the anterior head-region. In young stages the 
embryonic archenteron extends as a broad solid strand beneath that 
part of the brain which corresponds to the future thalamencephalon, 
and is continued on to the neuropore. This strand is soon divided into 
* Anat. Anzeig., xiii. (1897) pp. 161-70 (1 fig.). 
t Op. cit., xii. (1896) pp. 539-43. 
X Morpliol. Jalirb., xxiv. (1896) pp. 209-86 (4 pis.). 
