36 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
but tbe ovum may come from either ovary. There is only a slight 
majority in favour of the right ovary. 
The earliest stage in development which M. Duval observed was 
the four-cell stage. The cells resulting from the division of the micro- 
meres form the ectoderm and grow round the macromeres which form 
the endoderm. A meta-gastrula results — an external sphere of ectoderm 
and an internal mass of endoderm. But although the author meantime 
regards this as the gastrula, he admits the difficulty of establishing the 
homology, and promises to return to the subject. 
In a continuation * of the above memoir, Duval describes first the 
extension of the endodermic mass. The blastodermic vesicle becomes 
didermic, but this state does not at first exist in the inferior hemisphere, 
the centre of which remains for a time monodermic — that is to say, 
ectodermic. The formation of the amniotic mass is then discussed ; it 
begins as a massive thickening of ectoderm, but this, instead of being 
hollowed out by a closed central cavity, becomes irregularly broken 
and thereafter forms a cupola by folds of the familiar type. With the 
growth of the amniotic folds the appearance of a differentiated mesoderm 
is associated. 
The fixing of the ovum is accomplished by a process very like what 
occurs in Kodents and Carnivores. The ectoderm is closely applied to 
the uterine mucosa, whose epithelium has disappeared ; the ectoderm 
elements penetrate the mucous tissue and surround the capillaries, whose 
walls are remarkably modified. 
Gestation of Vespertilio niurinus.f — M. P. Nolf has investigated 
the modifications of the uterine mucous membrane which take place 
during the gestation of this bat. He finds that the muscular fibres at 
the level of the placenta tend to take, during gestation, a circular 
direction. In the glandular part of the mucous membrane the superficial 
layers of the dermis rapidly undergo necrosis, while the deeper layers 
are converted into an epithelium-like tissue, which is likewise destined 
to disappear later on. In the deeper region there is produced, before 
the reception of the blastocysts, a general vascular dilatation, which is 
accompanied by the formation of vessels. The uterine dermis is dif- 
ferently modified in the immediate neighbourhood of the placenta, and 
in the deeper layers in them there are formed two layers, an upper one 
which is called the paraplacental layer, and a deeper one which is called 
epithelioid. The latter has at first, however, a fibrous appearance. Its 
elements, after active proliferation, ultimately die down, necrosis begin- 
ning in the part which is in relation to the paraplacental layer. The 
cells of this latter layer are arranged in a way which differs at different 
stages of gestation. These variations are probably due to variations in 
the rapidity of the growth of the placenta. The vessels of this latter 
are surrounded by the plasmodioblast, with the exception of the largest 
vessels. The endothelial cells of the surrounded vessels fall into the 
vascular cavity at a time when they show no trace of degeneration, and 
they are carried away by the blood. The endothelium of the venous 
vessels undergoes considerable hypertrophy in parts ; its elements 
appear to be leucocytes. Later on, the modified cells of this endothelium 
* Journ. de l’Anat. Physiol., xxxi. (1895) pp. 427-74 (2 pis. and 2 figs.). 
f Bull. Acad. Beige, lxv. (1895) pp. 206-40. 
