104 A. A. W. HUBRECHT. 
on the uterine surface. The pregnant horn of Manis carries 
but one embryo at a time, as was noticed by Weber. For the 
external shape of the uterus and the very considerable size of 
the ovaries I may also refer to that publication. 
That the aspect of the foetal envelopes is not always that of 
fig. 44 is shown in fig. 45, which represents a stage of about the 
same age but of a symmetrical development. The spacious 
yolk-sac is situated, as was already noticed by Weber, against 
the lower concavity of this sac. The foetus enclosed in these 
envelopes will measure about 20 mm. in length from the vertex 
to the root of the tail; towards parturition it will have increased 
to the size of about 14 cm. from the centre of the skull to the 
root of the tail. 
Additional Considerations. 
Having terminated the description of the Spolia nemoris 
as at this moment they lie before me, I may be allowed to give 
a summary review of a couple of biological questions in their 
present stage towards the solution of which I hope in the first 
place to utilize the material collected. 
These questions were already mentioned in the introduction, 
and have reference to— 
I. The origin and morphological significance of the cell 
layers constituting the two-layered blastocyst of mammals. 
II. The origin, the minute anatomy, and the morphological 
significance of the placenta. 
I; 
Since the very youngest mammalian blastocyst has been 
studied by means of sections and with the aid of the improved 
methods of the last decades, our knowledge of those incipient 
stages has grown very rapidly. For these earliest contributions 
we are indebted to Rauber,! van Beneden,? Lieberkiihn,® 
1 “Die erste Entwickelung des Kaninchens,” ‘Sitzungsberichte der 
Leipziger Naturforschenden Gesellschaft,’ 1875, p. 103. 
2 ¢ Bulletin de l’Acad. de Belgique,’ t. 60, 1875, p. 686; five years later 
followed by ‘‘La formation des feuillets chez le lapin,” ‘ Archives de Biologie,’ 
vol. i, 1880. 
5 “ Ueber die Kleimblatter der Siiugethiere,” ‘ Gratulationsschrift Nasse,’ 
Marburg, 1879. 
