348 A. A. W. HUBRECHT. 
understood by constant reference either to preparations or to 
numerous drawings. And so an account of the relation in 
which certain results above described stand to those which 
have lately been obtained elsewhere has been reserved for this 
chapter. I will at the same time notice the points in which 
these different researches appear to agree and those in which 
further researches are necessary because of discrepancies 
or uncertainties. The results 1 wish more especially to discuss 
are in the first place those concerning the unexpected part 
which embryonic epiblast is seen to play, both in the ompha- 
loidean and in the allantoidean placentation, and in the second 
place the formation of lacunar blood-spaces without an en- 
dothelial lining, which appear in this epiblastic proliferation 
at a very early stage of development, and which are even then 
accessible to maternal blood, which is here brought into close 
and extensive contact with the young blastocyst. 
The first unmistakable account of such a process is given in 
Selenka’s ‘ Keimblatter und Primitivorgane der Maus’ (1883). 
His reference to the details of the process in the text is, 
however, exceedingly scanty. A circumstantial account of the 
mode of formation of the so-called Trager is given, but the 
process of its vascularisation is not further described. His 
figures are, however, most reliable guides, by which we may 
conclude that the process of epiblastic proliferation, combined 
with the formation in this epiblast of lacunar spaces that carry 
maternal blood towards the embryo, was clearly noticed by 
him. He has observed and figured this vascularised and epi- 
blastic ‘ Trager’ (for which I will henceforth employ the term 
trophodisc) in Arvicola arvalis, Mus musculus, decu- 
manus and sylvaticus, and in Cavia cobaya. In his 
third ‘ Heft’ (‘ Die Blitterumkehrung im Hi der Nagethiere ’) 
he says (p. 88) that the placenta embryonalis is identical 
with the Trager, which was regarded by all the earlier observers 
as formed of maternal uterine tissue (p. 84). Selenka’s claim to 
priority—incomplete as his description of the process may be— 
is fully recognised by Mathias Duval, who followed in his steps 
in 1887, with a more full account of the early stages in the 
