STUDIES IN MAMMALIAN EMBRYOLOGY. 381 
man after what the hedgehog has taught us. Special atten- 
tion ought in favorable cases to be given to the following 
questions : 
a. Can, in the very earliest stages of the human blastocyst, 
any trace be found of trophospheric tissue between the villi- 
ferous blastocyst and the inner surface of the decidua 
reflexa ? 
6. Are there blood lacune in this tissue which receive blood 
directly out of the. vessels that take their course in the tissue 
of the reflexa? 
ec. Can traces of trophospheric tissue be found in the region 
of the serotina?! Will the constituents of the full-grown 
human placenta, which are known as Winkler’s “ Schlussplatte” 
and as the “‘ sept placentz,”’ have to be regarded as embryonic 
trophoblastic or as maternal trophospongian elements ? 
If, indeed, the comparisons here advocated will prove to be 
well founded, the question about the epithelial remnants ad- 
hering to the fcetal villi that are freely bathed by the maternal 
blood in the placentary lacunz will once for all be decided in 
a different sense from what was first brought forward by Turner, 
1 While this MS. was being corrected for the press, No. 17 (September Ist, 
1889) of the ‘ Anatomischer Anzeiger’ came into my hands, in which Keibel 
describes sections through very early stages of the attachment of the human 
chorion frondosum against the maternal tissue. From his description and 
figures I gather that he looks upon the blood-spaces between these early villi 
as “kolossal erweiterte miitterliche Capillaren,’ thus confirming Turner’s 
interpretation. The woodcut accompanying his paper is certainly very 
decisive, but I am confident that the details there figured will allow of a 
different interpretation, when still earlier stages cau be drawn into comparison. 
Already a comparison between his woodcut and figs. 54—57 of this paper 
will prove instructive, and forces the suggestion upon us that the trophoblastic 
tissue of the hedgehog, in which so very spacious blood-lacune are present, 
but which after all forms a still dense network, is the equivalent of what 
Keibel once more designates as “ miitterliches Endothel.”” That the blood- 
spaces are homologous is self-evident. That in man they are comparatively 
larger still than in the hedgehog is not astonishing. Consequently the inter- 
vening trophoblastic tissue must have been reduced, and we cannot wonder 
at its finally assuming an endotheloid arrangement. With respect to the 
question in how far any equivalent of the hedgehog’s and the bat’s tropho- 
spongia may be found in the human subject, Keibel’s short note gives no clue, 
