448 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The author concludes that fecundation consists not only in the 
addition of two demi-centres arising from individuals of different sexes, 
but in the union of two demi-spermoeentres with two halves of ovocentres 
to form the two first astrocentres. All the succeeding astrocentres are 
derived in equal parts from the mother and the father. 
Comparative Anatomy of Placenta.* — Prof. E. Klebs has endea- 
voured to throw light on some unsolved problems by a study of the 
placenta in the white rat. From the distribution and appearance of the 
arteries and veins seen on a cross section of the gravid uterus, he argues 
that in the vascular layer of the maternal placenta there must be a slow 
circulation at relatively high pressure. The blood-stream finds its 
main outflow in the so-called peri-placenta. As the result of abundant 
nutrition, the maternal epithelium, the connective matrix, and the 
endothelium of the widened vessels are all hypertrophied. In the layer 
of the “ monster-cells,” as Minot calls them, the endothelial prolifera- 
tion closes the openings of the vessels, but this closing membrane is not 
impervious. It allows red blood-corpuscles to pass into the numerous 
clefts between the monster-cells, and these corpuscles are found in the 
space between maternal and foetal epithelium, and also between the 
serous membrane and the extension of monster-cells on the lateral 
regions of the placenta. During life there must be some way of securing 
that the blood in the important inter-epithelial space flows off. Klebs 
believes that this is secured by the layer of smooth muscle-fibres 
covering the internal surface of the vascular part of the maternal 
placenta, and he ventures to speak of a “ placental heart.” He compares 
the placenta in the rat with that in the rabbit, and with that in man ; 
all the three may be called vascular, for it is to elements of the vascular 
system that the chorionic villi become apposed ; but the details of 
vascular arrangement are different. The placenta may be called plexi- 
formis in the rabbit, cavernosa in manner appositionem in the rat. 
Placenta of the Cat.f — Prof. G. Henricius has corroborated by an 
investigation of the placenta of the cat some of the observations which 
he previously made in regard to that of the dog. Where the foetal 
ectoderm or chorionic epithelium begins to come into connection with the 
uterine mucosa, the superficial epithelium of the latter has disappeared. 
At this early stage the glandular cells are already much modified ; they 
give origin to material which passes through the superficial layer of 
connective tissue into the uterine cavity. Before or during the firmer 
fixing of the embryo there is a complete or almost complete closure of 
the uterine glands. The chorionic villi certainly do not penetrate at 
first into the glands, but enter the superficial connective tissue. As 
they penetrate deeper they are seen to be surrounded by a syncytium, a 
kind of decidua due to a modification of the connective tissue. Neither 
glandular epithelium nor foetal epithelium takes part in forming the 
syncytium. Most of it subsequently disappears, probably absorbed by 
the foetus. In the neighbourhood of the villi, the glandular cells 
undergo disruption, and perhaps help in the nutrition. Moreover, red 
blood-corpuscles seem to pass through the walls of the vessels, and 
* Arch. f. Mikr. Anat., xxxvi. (1891) pp. 335-56 (1 pi.). 
t Op. cit., xxxvii. (1891) pp. 357-74 (2 pis.). 
