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 placentse of other deciduate Mammalia assume an arborescent appearance by 

 maceration, as compared with the Human or with the Siraious placenta they present 

 ordinarily the appearance rather of interdigitating lamellae^ 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 Fcetus Canini velamentis. Mem. Acad. Scien. St. Petersbourg, torn. v. 1815: Isis, 1818, 



p. 1616. 

 G. Cuvier. Sur les Enveloppes du Foetus. Memoires du Museum, torn. iii. 1817. 

 Bojanus. De Fcetu Canino 24 dierum. Nova Acta, tom. x. 1821. 

 Rudolphi. Embryo der Affen. Abhandlung. Berlin Akad. 1828. 



Von Baer. Untersuchungen iiber die Gefassverbindung zwischen Mutter und Frucht. 1828. 

 C. G. Cams. Tabulae Anatoraiam Comparativam Illustrantes, iii. and v. 1831-1840. 

 Mayer. Nabelblaschen und AUantois. 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 Fcetus inserviunt. Hafnise, 1837. 

 Vou 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 ssepissime vidi quam tegumentum esse a tunica serotina prsebitum 

 nuUus dubito." — De Organis, p. 127. 



' Eschricht, I. c. pp. 14, 26 ; Von Baer, 'Gefassvorbindnng,' pp. 23 & 24. 



