316 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
first three or four weeks of its development lies free within its capsule. 
On the contrary, in the first w’eek of development it is firmly and per- 
manently united to the uterus, for the villi of the chorion grow into the 
openings of the uterine glands. Selenka bases this conclusion confidently 
on the results of his investigation of early stages both in apes and in 
man. Moreover, he urges the following considerations : — (1) If the 
ovum lie free for weeks, its encapsuling by the decidua is unintelligible, 
for this surely results from the stimulus of contact between ovum and 
uterus ; (2) if the ovum does not unite very early with the uterine 
epithelium, the latter should be demonstrable on the internal surface of 
the capsule cavity, but it is not ; (3) the supposition of a double-layered 
chorion ectoderm is unsupported by any analogy ; (4) except on Selenka’s 
conclusion, the early nutrition of the ovum is unintelligible. 
Development of Apes.* — Prof. E. Selenka has a preliminary notice 
of the results of his studies on the development of Apes. The most 
primitive type is to be sought for in those Apes in which the germinal 
vesicle is not surrounded by a decidua reflexa ; there are here two pla- 
centae, one on the dorsal surface of the foetus and the other on the 
ventral surface of the germinal vesicle. From this type two others 
have arisen independently ; in both the decidua reflexa forms a capsule 
round the germinal vesicle. If the reflexa contains both blood-vessels 
and uterine glands two discoid placentae are formed, but if these are 
wanting the second placenta remains quite rudimentary. 
The most primitive form, or placenta bidiscoidalis typica, is found 
in all Catarrhine Monkeys of the Old World, but not in Man or the 
higher Apes. The placenta bidiscoidalis circumvallata, which has, as 
yet, been seen only in Hylobates (the Gibbon), differs only from the 
typical in that the ventral uterine placenta does not arise from the 
ventral, but rather from the dorsal wall of the uterus. The placenta 
monodiscoidalis or discoidalis, which is found in the other Anthropoid 
Apes and in Man, must be regarded as homologous with the dorso- 
placenta of other Apes. 
Great as the differences in the placentation of the three types appears 
to be, those of the other embryonic membranes and of the foetuses them- 
selves are very slight. The rudiment of the placenta, for example, is 
always the same. A slight sketch is given of the developmental history 
of the Catarrhine Monkey Semnopithecus maurus. The general lesson is 
that, in Apes and Men some embryonic organs are developed earlier, 
and others later than in other Mammals. The precocious structures 
are the numerous chorionic villi, the coelomic sacs, and the stalk of the 
allantois. Those that are later are the yolk-sac, whose vascular plexus is 
not developed for some time, and which must be regarded as a vestigial 
organ ; the allantoic cavity is long in appearing. 
The characteristic points are the loose tissue of the somatopleure 
which lines the chorion, the persistent stalk of the amnion, the out- 
growth of the amnion and its fusion with the chorion, the vestigial 
nature of the yolk-sac, the formation of two opposed placentae, one of 
which may remain rudimentary, and the attachment of the non-placental 
part of the embryonic sac to the surrounding uterine wall. 
SB. K. Preuss. Akad. Wigs., 1890, pp. 1257-62. 
