290 PROFESSOR ROLLESTON ON THE 



Insectivora and Chiroptera. 



In the Hedgehog {Erinaceus europeeus), at a time wlien the foetus is about one-third 

 the size of that of the foetal Tenrecs here described, and the yelk-sac is as large as the 

 amniotic, the non-deciduous serotina is separable as a perfectly distinct and coherent 

 coat from the circular muscular coat which it overlies ; the deciduous serotina is a very 

 thick mass, bell-shaped, with its convex end attached to the non-placental mucous 

 membrane by a thin peripheral parapet, within which vessels and cellular tissue connect 

 it with the utero-placental area. Exteriorly to tlie attachment of the delicate parapet 

 of non-placental mucous membrane, the external surface of the deciduous serotina 

 becomes smooth, and it may here take the name of " decidua reflexa," whilst its internal 

 surface, in apposition with the ovum, remains rough and flocculent. The prolongation 

 of decidua serotina, or, in other words, the decidua reflexa, does not entirely encapsulate 

 the ovum, as we shall see that it does in certain Rodents, but falls short of doing so 

 by an interval homologous with the non-vascular umbilicus-like spot observable in the 

 decidua reflexa of the Human subject'. The entire structure inter-uteroplacentally and 

 extra-ovularly placed is bell-shaped, as compared with its wafer-shaped homologue in 

 the Tenrec, or its closed sac-like homologue in the early embryo of the Rat. The 

 decidua reflexa is sometimes spoken of as being an outgrowth of the decidua serotina^, 

 sometimes as being continuous rather with the decidua vera in the Human subject^. 

 What is of importance to bear in mind is, that the non-placental mucous membrane 

 becomes continuous at the periphery of the placental area with both non-deciduous and 

 deciduous serotina; and that from the point of its junction with this latter structure a 

 more or less extensive envelope grows outwards over the chorion, to which the name 

 " decidua reflexa" is given. The placenta at this period in the Hedgehog is a much 

 smaller structure than the deciduous serotina it underlies ; it is itself underlain by a 

 purse-shaped allantois like that of the Rabbit, which moors the amniotic sac and the 

 foetus it contains to one pole, whilst the yelk-sac moors it to the other pole of the 

 chorion. As in the early foetus of the Dog, so in that of the Hedgehog at this period, 

 it is possible by maceration to separate entirely, or nearly so, the foetal villi growing on 

 the allantoic area of the chorion from the maternal elements, which shortly after 

 become inextricably interfused with them to form the " placenta." 



In a Shrew {Sorex, sp. ?), the foetus being at an early stage of development, and only 

 three eighths of an inch long, the deciduous serotina was, as in the Hedgehog, about 

 three times the size of the placenta proper. I did not satisfy myself that it was pro- 

 longed into a decidua reflexa : that it was so is rendered improbable by the fact that the 

 other membranes were drawn out at either end into slender tubular processes of an 

 eighth of an inch in length, beyond the subglobular space occupied in the uterine cornu 

 by the foetus. Its structure was coarsely columnar ; that of the placenta presented a 

 villous appearance. The placentae were attached to the free border of the uterine cornu. 

 ' KoUiker, I. e. pp. 178, 181. '- Ibid. p. 142. = Robin, I.e. p. 131. 



