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SUMMARY 
OP CURRENT RESEARCHES RELATING TO 
ZOOLOGY AND BOTANY 
( principally Invertebrata and Cryptogamia ), 
MICROSCOPY, Ac., 
INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS.* * * § 
ZOOLOGY. 
A. VERTEBRATA : — Embryology, Histology, and General. 
a. Embryology, t 
Theory of the Structure of the Placenta.f — Mr. C. S. Minot’s 
theory may be shortly summarized thus : — He looks upon the placenta 
as an organ of the chorion ; primitively the chorion had its own circu- 
lation and formed the discoidal placenta by developing villi which 
grew down into the degenerating uterine mucosa ; by the degeneration 
of the maternal tissues the maternal blood is brought closer to the villi, 
and the degeneration may go so far that all the tissue of the uterus be- 
tween the villi disappears. A layer of the mucosa is preserved between 
the ends of the villi and the muscular layer of the uterus to form the 
so-called decidua ; the placenta receives its foetal blood by the means 
of large vessels running in the mesoderm of the allantois. From this 
discoidal chorionic placenta the zonary placenta of Carnivora, the diffuse 
placenta of the lower Primates, and the metadiscoidal placenta of Man 
have been evolved. 
A second type of placenta, perhaps evolved from the first, is found 
in Ungulates, and is characterized by a vascular allantoic vesicle uniting 
with a now vascular chorion to form the foetal placenta, and by the 
absence of degeneration in the maternal tissue. This is the allantoic 
placenta. 
First Stages of Placental Union in Man.§ — Prof. E. Selenka brings 
forward evidence against the general opinion that the ovum during the 
* The Society are not intended to be denoted by the editorial “ we,” and they do 
not hold themselves responsible for the views of the authors of the papers noted, 
nor for any claim to novelty or otherwise made by them. The object of this part of 
the Journal is to present a summary of the papers as actually published , and to 
describe and illustrate Instruments, Apparatus, &c., which are either new or have 
not been previously described in this country. 
f This section includes not only papers relating to Embryology properly so called, 
but also those dealing with Evolution, Development, and Reproduction, and allied 
subjects. 
% Anat. Anzeig., vi. (1891) pp. 125-30. 
§ Biol. Centralbl., x. (1891) pp. 737-44. 
