340 A. A. W. HUBRECHT. 
actually filled with maternal blood, was repeatedly established 
by me by the aid of injections. These were made both with 
blue and red gelatinous injection-masses that were introduced 
into the crural artery of the mother. I have specimens thus 
injected belonging to stages of diagrams 29, 30, 33, and 35. 
The two earlier stages are especially instructive for what we 
are discussing at present. After having preserved the injected 
specimens in alcohol and having hardened them sufficiently, a 
section through the uterus and the middle of the blastocyst opens 
a free insight into the yolk-sac. We then notice that the hollow 
surface of the trophosphere is of a deep red tint, the injected 
mass being only separated from the yolk-cavity by two cell- 
layers, the trophoblast and the hypoblast. There was no trace of 
injection mass inside the yolk-sac, and not the least reason to 
suppose that the red colour alluded to was due to an extrava- 
sate. Microscopic sections confirmed this, and the way which 
the injection mass had taken along the mesometrical arteries 
upwards towards the centre of the decidual proliferation, from 
thence along the wide vessels of this modified portion of the 
mucosa towards the lacune of the trophospongia, and from 
there into the spaces of the trophoblast, can be most accurately 
traced. Even the backward flow by venous channels was made 
distinct by the injection mass, which, however, did not fill 
these spaces as it did the arteries, but was here only distributed 
to a certain extent amongst the maternal blood-corpuscles. 
The fact of the early presence of a copious flow of maternal 
blood in those spaces of which the figures 89—42 represent the 
early developmental stages is thus established beyond any 
doubt. We must in consequence assume that this maternal blood 
contributes to the growth and development of the blastocyst 
even long before an embryonic circulation has been established. 
How it achieves nutritory functions cannot with certainty be 
stated, nor whether it directly contributes to the accumulation 
of any nutritory fluid inside the yolk-sac. We can better picture 
to ourselves its mode of action at the moment the area vascu- 
losa has become established, and when there is thus only a 
thin partition between the vitelline circulation and the maternal 
