STUDIES IN MAMMALIAN EMBRYOLOGY. 323 
Already in preparations as that of fig. 42 (diagram 29) the 
trophosphere may be detected with the naked eye on holding 
the section against the light. 
In later stages this is of course still more emphatically the 
case. And the name here given to that region has, besides its 
convenience, the advantage of indicating that in the whole of 
the spherical region thereby designated special arrangements 
for the nutrition of the very youngest blastocysts have very 
rapidly developed, independently of what will later be the 
phenomena of placentation, omphaloidean or allantoidean. 
We must acknowledge that a spherical] arrangement, as 
present in Erinaceus, is rare (Primates?), whereas correspond- 
ing regions of the rabbit might be indicated by the name of 
trophodisc, that of the bat and mole of trophocalyx, &c. The 
use of the name placenta must in these early stages inevitably 
lead to confusion, and yet a designation is necessary to indicate 
that nutritory arrangements have been established between 
the blastocyst and the maternal circulation. 
In the early developmental stages of the trophospongia, of 
which fig. 42 is an example, the trophospongia is very compact, 
although blood lacunz between the cells, communicating cen- 
tripetally with the widened and flattened spaces of the tropho- 
blast and centrifugally with the blood-cavities in the decidual 
tissue, are unmistakably present, and contain maternal blood- 
corpuscles. The blood cavities in the rest of the decidual 
tissue that has not undergone the modification described as 
the trophospongia, and which were uot as yet visible in stage 
fig. 87, make their appearance and become very conspicuous 
soon after the stage of figs. 39 and 40 has been reached. The 
vasifactive tissue noticed in fig. 87 has expanded, numerous 
and spacious lumina are bounded by an endothelium, which is 
not flattened but very distinct, the cells more or less bulging 
out into the lumen, though not so prominent as the endo- 
thelium of the vessels close to the blastocyst, from which the 
trophospongia has originated. 
The general change brought about when the decidual swell- 
ing 1s no longer a wholly compact mass, but is everywhere 
