84 ON THE PLACENTAL STRUCTURES OF THE TENREC 



coating on the utero-placental'zone. Bojanus (1. c. p. 143) speaks 

 of it in comparison with the non-placental mucous membrane, as 

 ( crassiorem, floccosam, leviter spongiosam, et cellulis distinctam 

 hiantibus ubi primum foetus suis velamentis ab utero distrahitur.' 

 Next to it we find a membrane separate alike from placenta below 

 and non-deciduous serotina exteriorly, presenting the appearance 

 of a circular honeycomb work, the depth of the more or less regu- 

 larly polygonal cells being from the fifth to the eighth of an inch 

 in depth, and of about the same diameter. This membrane readily 

 peels away from the placenta proper, at all events from a specimen 

 which has been for some time in spirit; and the surface of this 

 latter envelope is now seen to be also obscurely mapped out into 

 polygonal spaces. These spaces, however, are not empty, as are 

 the honeycomb membranes just described, but their periphery is 

 filled up with cellular elements belonging to the maternal organism, 

 whilst in the centre of each is to be seen the summit of the 

 mushroom-shaped upgrowths from the chorion. These two ele- 

 ments may, as already remarked in the case of the hedgehog, be 

 separated from each other with some little trouble * ; at a later 

 period they not only become inextricably fused with each other, 

 but, growing upward and into the honeycomb layer of decidua 

 serotina, they cohere inextricably with it also, and bring it away 

 with them at parturition, as already described. It is perhaps 

 remarkable that the decidua serotina should retain its distinctness 

 in the cat; its alveolar character, however, is not of the same 

 coarseness as that of the homologous membrane in the dog, and 

 the greater relative abundance of all the other elements, and the 

 smaller consequent size of the honeycomb vacuoles, may account 

 for the maintenance by it of an independent existence up to the 

 time of parturition. It exists, however, in the cat at full time 

 rather as a separable than as a coherent layer. In the dog it is 

 neither coherent nor separable from the placenta 2 . 



It is difficult to see how, with the honeycomb-like decidua 

 serotina of the foetal dog before one, placed in relation with 

 the mucous membrane of the unimpregnated and unenlarged uterus 



1 Bischoff, 'Hunde Ei,' p. 114. 



2 It would seem from Barkow's description of the foetal membranes of a seal 

 (Phoca vitulina), that the decidua serotina possesses both these characters in that 

 animal (Zootomische Bemerkungen, 1851, p. 7). 



