EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 121 
which, when once the regular passage of maternal blood 
into the trophoblast has been firmly and safely established, 
all these preparatory processes as far as the mother is con- 
cerned come to a standstill, the further elaboration of the 
placenta being exclusively a function of the trophoblast and 
of the embryonic blood-vessels or vascular allantoic vill, 
which gradually have become imbedded in and ensheathed 
by the trophoblast. 
In short, we may say that the mutual relations between 
maternal trophospongia and embryonic trophoblast are such 
that the maternal trophospongia leads up to the formation of 
a hemorrhage, and that the embryonic ectoplacenta (itself a 
trophoblastic proliferation), succeeds in surrounding this 
hemorrhage most thoroughly and in utilising it most: fruit- 
fully. It was Duval (’89—’92) who first established this 
comparison. 
a. Insectivora.—For the hedgehog we have in the pre- 
ceding chapter given a full account of the phenomena 
accompanying the attachment of the blastocyst. We will 
here add a few facts concerning the maternal preparation for 
the placentary attachment. 
Already on p. 102 the local swelling was noticed into the 
median pit-like cavity of which the early blastocyst disap- 
pears. ‘These swellings arise after impregnation but inde- 
pendently of a local stimulus caused by the blastocyst, as I 
have more than one preparation in which the swelling is 
present but does not include a blastocyst. Another detail 
which proves the relative independence of these swellings is 
the very fixed and regular appearance of a limited hemor- 
rhage occurring at the lips of the swellings such as have 
been described by myself and by Resink, and by which the 
final closure and the completion of the decidua reflexa is 
broughtabout. Characteristic features of the trophospongean 
swellings here described are yet the following. ‘They arise 
in the antimesometrical half of the mucosa and have the 
aspect of a spherical knob with an incisure on its free 
surface, the direction of which is parallel to the axis of the 
