298 PROFESSOR ROLLESTON ON THE 



The persistent or non-deciduous serotina in the Guinea Pig is inseparable, save to the 

 eye aided by the microscope, from the circular muscular coat. 



BischofF says ' of the decidua serotina, that it separates from the regenerating mucous 

 coat immediately after the separation of the placenta, and is either discharged or, as he 

 thinks, in many cases quickly absorbed ; and Reichert'^ believes that certain structures 

 found not rarely in the uteri of pregnant Guinea Pigs may be the remnants of the 

 placenta uterina and decidua reflexa of previous pregnancies. I have no observations 

 of my own with reference to what takes place in the natural order of things, but in the 

 after-births of Guinea Pigs killed at full time I have found the deciduous serotina in 

 some cases so firmly cohering with the placenta and with the upgrowth of it (pl') as to 

 make it difEcult to believe that it does not occasionally come away with it in par- 

 turition, as by actual observation we know it does in the Rat. Variations may occur 

 in the case of the former animal. 



The Guinea Pig and Rat resemble each other in having, in early stages of develop- 

 ment, a perfect decidua, in having their chorion attached to the centre of a unilobed 

 placenta, and in having the sac of the allantois early obliterated ; and in all these 

 points they differ from the Leporidse. 



The circlet of vascular villi lying exteriorly to the placental area, and supplied exclu- 

 sively by the omphalo-mesenteric system, is said by BischofF^ to spring up only in the 

 latter part of foetal life. In those Rodents in which, as in the Muridse and in the 

 Guinea Pig, the chorion is attached by an apex, as it were, to the centre point of the 

 floor of the placenta, we see, on making a transverse section of a uterine dilatation 

 containing an advanced foetus, that a considerable interval exists on either side of the 

 attachment of the chorion to the after-birth, along which any matter secreted by the 

 uterine mucous coat can pass. And it is precisely over the part of the chorion which 

 forms one side of this triangular space that these villi spring up, according to BischofF, 

 in the later stages of pregnancy — at a period, that is, in which the non-vascular non- 

 secreting decidua reflexa is absorbed, and the secretion of the non-placental mucous 

 membrane, whatever it may be, can be brought into relation with, and absorbed by, the 

 foetal vessels. This appears to be a very beautiful instance of natural economy. In 

 the Leporidse, it is true, the chorion is not attached to the centre of the placeutulse, and 

 it therefore has not that partial protection from the pressure of the uterine walls for the 

 omphalo-mesenteric circlet of villi which the placentae of the Rodents we have been 

 speaking of enjoy ; but as their decidua reflexa is but a rudimentary fringe (fig 7, d r), 

 whatever is secreted by the uterine walls can at all limes come into immediate relation 

 with the omphalo-mesenteric vessels, and be absorbed by, or interchange products with 

 them. 



In no Rodent that I have examined is the non-deciduous serotina separable as a 

 distinct and coherent layer from the circular muscular coat ; in all Rodents the placental 

 ' Meerschweinchen-Ei, p. 44. ^ Beitrage, p. 131. ° Meerschweinchen-Ei, pp.43 & 44. 



