114. A. A. W. HUBRECHT. 
tion that precocious segregation of part of the hypoblast comes 
into play and that we have to distinguish a coenogenetic and a 
palingenetic hypoblast. This suggestion has been favorably 
received ; the natural counterpart of it is the above sketched 
precocious segregation of part of the epiblast. Both are adapta- 
tions to similar external conditions. 
if, 
The origin, the minute anatomy, and the morphological 
significance of the placenta have been of late inquired into by 
a considerable number of independent investigators. It may 
suffice to cite among the more recent ones Duval, Strahl,’ 
Frommel,’ Fleischmann,‘ van Beneden,® Masius,® Lisebrink,’ 
Heinricius,? Minot,? Hubrecht,!° and others. Questions that 
were more particularly entered into are those that concern the 
fate of the maternal epithelium at the spot where the blasto- 
cyst comes to adhere against the uterine surface. In Erinaceus 
it undergoes changes that are very different from those that 
take place with it in the rabbit, and different again from what 
happens with it in the Carnivora. In Sorex the fate of the 
1 M. Duval, ‘‘ Le Placenta des Rongeurs,’ Paris, 1889-93. 
2 H. Strahl, ‘‘ Untersuchungen iiber den Bau der Placenta,” I—ILV, 
‘Arch. f. Anat. u. Physiol.,’ 1889, 1890. V. Anat. Hefte von Merkel u. 
Bonnet, 1892. 
3 R. Frommel, ‘ Ueber die Entwickelung der Placenta bei Myotus murinus,’ 
Wiesbaden, 1888. 
4 A. Fleischmann, ‘ Embryologische Untersuchungen,’ Hefte 1—3, Wies- 
baden, 1889-93. 
5 i. v. Beneden, “De la formation et de la constitution du placenta chez 
le Murin,” ‘ Bull. Acad. roy. Belg.,’ 3¢ ser., t. 15, 1888. 
6 J. Masius, “De la genése du placenta chez le lapin,’ ‘Archives de 
Biologie,’ vol. ix, 1889. 
7 ¥. W. Liisebrink, ‘‘ Die erste Entwickelung der Zotten in der Hunde- 
placenta,” Anat. Hefte von Merkel u. Bonnet, ii, 1892. 
8 Heinricius, ‘‘ Ueber die Kutw. u. Struct. d. Placenta beim Hunde,” ibid. 
“bei der Katze,” ‘ Arch. f. mikr. Anat.,’ Bde. 33 u. 37. 
9 C.S. Minot, “ Uterus and Embryo,” ‘Journal of Morphology,’ ii, 1889. 
10 Hubrecht, “ Erinaceus,” ‘Quart. Journ. Mier. Sci.,’ xxx, 1889 ; “Sorex,” 
ibid., xxxv, 1894; and ‘ Verhandel. k. Akad. v. Wetensch. Amsterdam,’ 
2¢ Sec., vol. iii, 1893. 
