126 A. A. W. HUBRECHT. 
invests as much as three-quarters of the surface (Fig. 159) 
of the blastocyst, but does not close up to a full decidua 
capsularis. The sequence and the histological detail of the 
phenomena are to a great extent comparable to what we saw 
in the hedgehog; for the details the authors above cited 
should be consulted. 
For the Carnivora, Duval (94, 795), Bonnet (’97, 701), 
Schoenfeld (03) and others have furnished us with reliable 
data. Here, again, the definite placenta is a structure of 
embryonic derivation, which partly eats its way in the sym- 
plasmata resulting from the degeneration of the epithelium of 
the uterine glands. More so than in other orders of mammals 
certain maternal elements persist (see above, p. 108), though 
enclosed by the trophoblastic syncytium; it is even stated that 
the endothelium of the maternal capillaries is not destroyed, 
as is the case in so many other mammals. In this respect the 
arrangement in Hrinaceus is more thorough. 
Coming to the Rodents, Schoenfeld (’05), whose important 
researches have been alluded to above, has lately compared 
the rabbit with the dog, and comes to the conclusion that 
they have very much in common, the rabbit’s placenta being, 
however, discoid, the dog’s zonary. As to the histological 
differences, both show trophospongial (maternal) and tropho- 
blastic (embryonic) preparatory processes before the blasto- 
cyst becomes attached to the uterine wall; after that the 
maternal epithelium is destroyed in the rabbit yet more fully 
than in the dog, also as concerns the endothelium of the 
maternal capillaries, which in the rabbit decidedly disappears 
under the destructive agency of the trophoblast-cells or their 
derivates. 
In the other Rodents we have already noticed the so-called 
Trager as a particular trophoblastic proliferation against 
which, after certain further cellular intermingling with 
maternal trophospongian elements the allantoidean placenta 
comes to be developed. ‘The combined action of trophoblast 
and trophospongia brings about spacious lacune round the 
blastocyst in the earlier stages of pregnancy. In these lacunz 
