STUDIES IN MAMMALIAN EMBRYOLOGY. 379 
blastocyst is said to commence only when the discoid placentary 
region commences to accentuate itself by a more intimate con- 
nection between foetal villi of the chorion frondosum and 
maternal tissue. The well-known and spacious placentary 
blood lacunze in which the branched villi are suspended 
characterise the ulterior stages of this developmental scale. 
We have now to consider whether the phenomena we have 
come to be acquainted with ‘in the hedgehog are not also sug- 
gestive with respect to those here referred to. In my opinion 
they are highly so, and I will now proceed to develop this 
more fully. At one time I received a pregnant hedgehog, the 
embryos of which proved to be in a stage of development 
corresponding to a stage between diagram figs. 31 and 32. 
The stage may be said to agree more or less with that of the 
early human embryos of two or three weeks (Reichert’s 
embryo and others). But, whereas I have been able to obtain 
all my embryos quite fresh from the live animal immediately 
after having administered chloroform, the animal in question 
had been dead several hours before I could extract the embryo 
from the spherical cavity in the proliferated decidua where it 
rested. I was very much struck by noticing, on dissecting 
away the decidua reflexa, that the blastocyst seemed to be very 
loosely attached to its surrounding, very much more so than I 
have ever noticed it in any blastocyst that was investigated 
when absolutely fresh. The blastocyst was nevertheless an 
elastic, more or less villiferous spherical body, and to its 
surface the remnants of the trophosphere still adhered, so that I 
have no doubt that what I enucleated was not the blastocyst 
pure and simple, but the blastocyst and trophosphere, i.e. the 
darker shaded sphere indicated in diagrams 31 and 32. The 
great facility with which, in this case, the embryonic tissue 
and its immediate surroundings were detached from the decidual 
proliferation I have no doubt whatever in ascribing to post- 
mortem processes, which immediately affect these exceedingly 
delicate cellular tissues, the more so as they are in all directions 
excavated by the blood-cavities above described. 
I was immediately reminded of the statement that the human 
