PLACENTAL STRUCTURES OF THE TENREC. 311 
demonstration of an arborescent placenta being, in both cases alike, the washing away 
of the intervillularly placed maternal substances’. For, though it may be possible to 
make the placentz of other deciduate Mammalia assume an arborescent appearance by 
maceration, as compared with the Human or with the Simious placenta they present 
ordinarily the appearance rather of interdigitating lamelle* than that of intertwining 
trees. 
From the facts given in this paper, imperfect as it is from the want of certain 
materials specified, as well as from other causes, it may seem to result that the modifi- 
cations of the placental structures form a very safe basis for the classification of the 
Monodelphous Mammalia. 
Why within the limits of so well-defined a class such wide variety should exist in the 
means by which is carried on and out that intra-uterine life which every member of the 
class lives alike, it is difficult for us to understand; but that such variety does exist 
there is no doubt. 
Differences, however, in structural arrangements which do exist, without our being 
able to see why they should exist, possess a morphological value which rises in direct 
proportion with their physiological obscurity. 
Bibliography. 
The following list gives the names of a number of books and memoirs which may 
be consulted with reference to the subjects treated of in this paper. They are arranged 
in the order in which they appeared :— 
Bojanus. De Foetus Canini velamentis. Mém. Acad. Scien. St. Pétersbourg, tom. v. 1815: Isis, 1818, 
p- 1616. 
G. Cuvier. Sur les Enveloppes du Foetus. Mémoires du Muséum, tom. iii. 1817. 
Bojanus. De Fretu Canino 24 dierum. Nova Acta, tom. x. 1821. 
Rudolphi. Embryo der Affen. Abhandlung. Berlin Akad. 1828. 
Von Baer. Untersuchungen iiber die Gefiissverbindung zwischen Mutter und Frucht. 1828. 
C. G. Carus. Tabulee Anatomiam Comparativam Illustrantes, iii. and v. 1831-1840. 
Mayer. Nabelblaschen und Allantois. Nova Acta, tom. xvii. pt. 2. 1834. 
Weber. Die Verbindung zwischen Mutter und Frucht. Froriep, Notizen, 996, Bd. 45, Oct. 1835. 
Eschricht. De Organis qui respirationi Foetus inserviunt. Hafniz, 1837. 
Von Baer. Entwickelungsgeschichte, vol. ii. 1837. 
Owen. Hunterian Catalogue, Phys. Series. 1840. 
Sharpey. Miiller’s Physiology, translated by Baly. 1842. 
Bischoff. Kaninchen-Ei. 1842. 
* Eschricht’s words as to this intercellular substance are exceedingly apposite: —‘Villos microscopii ope 
examinans massa grumosa eos obtectos esse seepissime vidi quam tegumentum esse a tunica serotina preebitum 
nullus dubito.”"—De Organis, p. 127. 
* Eschricht, /.c. pp. 14, 26; Von Baer, ‘ Gefissyerbindung,’ pp. 23 & 24. 
