IMBEDDING OF THE OVUM 
41 
that it is in two portions, would, if our view be correct, find a ready 
explanation. 
The ovum now rapidly differentiating develops a thick trophoblast 
all round the blastocyst as in the hedgehog, and not at one point as 
in the other species (see Figure vi, p. 33). The ovum is at first free 
in the implantation cavity. The trophoblast from a very early stage, 
n.z. pi. cyt. P.e. cyt. pi. n.z. 
Figure VII. Diagram op Teacher-Bryce Ovum. Magnified 50 d. 
(T. H. Bryce, del.) 
P.e., point of entrance; cyt., cyto-trophoblast; pi., plasm odi-troph oblast; 
n.z., necrotic zone of decidua; <jl., gland; cap., capillary; pi.', masses of 
vacuolating plasmodium invading capillaries. The cavity of the blastocyst is 
completely filled by mesoblast, and imbedded therein are the amnio-embryonic 
and entodermic vesicles. The natural proportions of the several parts have been 
strictly observed. 
as in the bat (Van Beneden), shows a cellular layer (cyto-trophoblast) 
and a plasmodial layer (plasinodi-troplioblast). The plasmodium throws 
out buds which stretch towards the walls of the decidual chamber, and it 
is continually being added to by active proliferation in the cellular layer. 
In the first place the plasmodial masses exert mainly a destructive action ; 
this results in the production of a relatively large implantation cavity such 
as seen in our specimen (Figure vn). The destruction of the decidua 
F 
