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SUMMARY OF CURRENT RESEARCHES RELATING TO 
internal bulging portion, which remains attached to the peripheral 
epiblast of the blastocyst along a circular lino, until the amnion is 
formed. Soon after the establishment of the mesoderm, the separation 
of somatic and splanchnic layers is distinguishable, the former follow- 
ing the contours of the epiblastic disc, and folding up all along the 
circular attachment above mentioned. The epiblastic fold of the amnion 
is not double, but a single sheet, accompanying the double fold of 
mesoblast. 
The germinal cell-mass bulges out gradually, leaving a central 
cavity, much in the same way as a morula becomes a blastula. The 
difference between this procedure and that described for the mole, rabbit, 
and opossum, is explained in reference to the fact that the cubic size 
of the hedgehog’s blastocyst is many hundred times less than that of the 
others. As to physiological facts, Hubrecht maintains: — (1) That 
peculiar nutritive facilities are afforded by the didermic blastocyst 
before the formation of vascular areas on yolk-sac and allantois ; (2) 
the “ serous envelope,” arising as a double layer of epiblast and meso- 
blast simultaneously with the amnion, does not as such take any 
important part in preparing the above facilities ; (3) the outer cell-layer 
of the didermic blastocyst contributes very actively to bring them about ; 
and (4) has an extensive and important role in perfecting the nutritive 
functions of the omphaloidean and allantoidean regions. 
The author then introduces a series of new terms, by which he hopes 
to facilitate discussion. The trophoblast is the epiblast of the blastocyst 
so far as that has direct nutritive significance, as indicated by prolifera- 
ting processes, and by immediate contact with maternal tissue, blood, or 
secreted material. The mesoblast, along with the trophoblast, forms 
the diplotroplioblast. That portion against which the vitelline circu- 
lation is applied is distinguished as omphaloidean from the mediodorsal 
allantoidean region. The omphaloidean placenta increases for a period, 
but retrogresses whenever the allantois begins to spread. Most im- 
portant is Hubrccht’s conclusion that both yolk-sac and allantois enter 
into very intimate interlocking, not with any maternal tissue, but with 
purely embryonic cell-material — the trophoblast — which has numerous 
lacunae filled with maternal blood, and is connected with the maternal 
tissue long before the appearance of either vitelline or allantoidean 
circulation. 
II. The Histological Modifications in the Uterine Tissues . — Where 
blastocysts are attached to the uterine wall, the lumina of the glands 
become occluded, the glandular epithelium gradually disappears, vascu- 
lar channels and capillaries develope strongly. At first the blastocyst 
reposes at the bottom of a groove, in free communication with the lumen 
of the uterus, but the opposite walls of the depression fuse, a haemor- 
rhagic clot fills up the entrance of the cup thus formed, and the result 
is a capsule homologous with the decidua rejlexa of the human subject. 
The blastocyst seems almost to eat its way into the maternal tissue, the 
uterine epithelium undergoing retrogressive metamorphosis. Round 
about the blastocyst, in the “vasifactive stroma” of the uterine mucosa, 
blood-spaces are formed in a unique fashion, and that region of mucosa 
undergoes proliferation and other changes, becoming the so-called 
“ decidua.” The zone of modified tissue with blood-cavities between the 
