358 A. A. W. HUBRECHT. 
in mitotic phases. In this superficial layer no cell-boundaries 
can be observed. 
“Tt is by this superficial layer that the union is brought 
about to the projecting surface of the uterine mucous layer; 
this layer undergoes an enormous development and forms a 
protoplasmic multinuclear mass into which the deeper epi- 
blastic layer sends out primordial papille which are in the 
beginning non-vascular and formed of epiblast, and of somatic 
mesoblast. Maternal blood-capillaries penetrate into the 
nuclear protoplasm of embryonic origin, and very soon lose 
their endothelium, and are further continued into a system 
of lacune that have no proper wall and are extremely 
numerous. 
“The allantois after it has soldered with the serous mem- 
brane vascularises the primordial papille by providing them 
with an axis of connective tissue, rich in blood-vessels. But 
at this moment the deeper layer of epiblast disappears partly 
around the axes of these allantoic villosities, and in conse- 
quence of this the maternal blood of the placenta, circulating 
in large lacunary spaces, is separated in many places from the 
vascular villosities by a layer of varying thickness of epiblastic 
multinuclear protoplasm. 
“Tt follows from our observations that the placenta of the 
rabbit is a neo-formation of foetal origin, formed by allantoic 
villosities, ramifying in a tissue which solely takes its origin 
from the epiblast of the embryo. This neo-formation is 
soldered to the stroma of the mucosa, the vessels of which 
have formed a system of lacune that perforate a protoplasmic 
multinuclear mass, that is not divided into separate cells and 
that owes its origin to a very considerable increase in thickness 
of the superficial layer of epiblast. In the placenta the maternal 
blood thus circulates in an epiblastic mass of embryonic origin.” 
I have entered at greater length into Masius’ description of the 
rabbit’s placenta, because he is more circumstantial than either 
van Beneden or Duval, and because from his description the 
points of resemblance between the phenomena that take place 
in the trophodisc of the rabbit and in the trophosphere of the 
