108 ON THE PLACENTAL STRUCTURES OF THE TENREC 



stages of pregnancy, without leaving much of the injection in- 

 extricably interfused with the foetal villi, whereas it is perfectly 

 possible to do this with the ruminant placentulae at any period. 

 The foetal villi of a placenta may be ' long, delicate, and branched, 

 giving a flocculent appearance to the small portion of the centre of 

 the dial by which the foetal placenta is attached to the womb 1 ; ' 

 but it is difficult to see how by this peculiarity they come to 

 resemble ' the foetal portion of the cotyledon in the cow,' unless it 

 could be shown that the uterine vessels when injected in a fresh 

 specimen left none of their own substance or of the tissue sup- 

 porting them interblended organically with the foetal upgrowths. 

 This can be shown in the ruminants. The delicate arborescent ap- 

 pearance which is described in the placenta of Pteropus is due, in 

 all likelihood, to the prolonged maceration in spirit to which a 

 pregnant uterus of an animal of its geographical distribution 

 would in all likelihood be subjected, and it may be paralleled by 

 the appearance which the human placenta, when similarly treated 

 for the purpose of showing its villous structure, may, in most 

 museums, be seen to wear. So far, therefore, from approximating 

 a chiropterous animal to the Pecora of Linnaeus, the placental 

 peculiarity brings them, as Linnaeus did bring them, into the same 

 class as the Primates — the necessary preliminary for the demon- 

 stration of an arborescent placenta being, in both cases alike, the 

 washing away of the intervillularly-placed maternal substances 2 . 

 For though it may be possible to make the placentae of other 

 deciduate Mammalia assume an arborescent appearance by macer- 

 ation, as compared with the human or with the simious placenta 

 they present ordinarily the appearance rather of interdigitating 

 lamellae 3 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 modifications of the placental structures 

 form a very safe basis for the classification of the Monodelphous 

 Mammalia. 



1 'Phil. Trans.' for 1857, p. 351. 



2 Eschricbt's words as to this intercellular substance are exceedingly apposite : 

 1 Villos microscopii ope examinans massa grumosa eos obtectos esse saepissime vidi, 

 quam tegumentum esse a tunica serotina praebitum nihil dubito.' — De Organis, 

 p. 127. 



3 Eschricht, 1. c. pp. 14, 26 ; Von Baer, ' Gefassverbindung,' pp. 23 and 24. 



