STUDIES IN MAMMALIAN EMBRYOLOGY. 385 
trophoblast (see p. 298), the outer layer plus a thin layer of 
somatic mesoblast without blood-vessels as diplotrophoblast 
(=v. Baer’s serous envelope), the portion of the diplotropho- 
blast against which the yolk-sac with its area vasculosa adheres 
as omphaloidean diplotrophoblast, that against which the allan- 
.tois does the same as allantoidean diplotrophoblast, then we 
have avoided misunderstandings that might arise from the in- 
discriminate use of the term chorion, and still we have not 
burdened science with many new names (cf. tabular view 
appended to this memoir). 
I feel convinced that in doing as I propose, astride would be 
made towards greater lucidity, both in the teacher’s expressions 
and in the student’s brain. The fact that original investiga- 
tors of mammalian embryology will be less liable to suffer 
from insufficient or misleading nomenclature is no excuse for 
postponing a salutary improvement of nomenclature. 
There is no necessity to suppose—as many authors do—that 
in those very early human blastocysts in which no trace of an 
embryo was found, and which, nevertheless, had a vascular 
villiferous chorion, the embryo must necessarily have under- 
gone retrogressive degeneration, the product of which is a 
gelatinous layer applied against the blastocystic wall! His 
has already combated this proposition (l.c., p. 173), and a 
glance at diagrams 31 and 32 of the hedgehog will facilitate 
the assumption that in man the layer in question may actually 
be the vascular somatic mesoblast, which develops so early, 
fusing with the trophoblast and becoming vascularised in a 
way which may perhaps prove to coincide with the hypothetical 
sketch above traced. 
It should be distinctly understood that the hypothetical 
interpretations of the human chorion here given, corresponding 
“Tch [werde] die dussere Ektodermlage der Keimblase einfach als 
‘Chorion’ bezeichnen...... Hine Nomenklatur, welche sich auf die 
verschiedene histologische Struktur der aussersten Hihiille griinden wollte, 
begegnet besonders bei einer vergleichenden Betrachtung so viele Schwierig- 
keiten, dass es nicht der Miihe lohnt, etymologische Kunststiicke zu ver- 
suchen” (Fleischmann, ‘ Embryologische Untersuchungen,’ Heft i, S, 61,) 
