310 PROFESSOR ROLLESTON ON THE 
structures over that area, which perfect regeneration, however, we do find to take 
place in the whole class of deciduate mammals. Nor is this all. For though the 
structures lettered px and pu’ in fig. 4 might be taken to represent, though roughly, the 
cotyledons on the discharged placenta of a Ruminant, the structures which they were 
drawn from in the Rodent differ essentially from the placentulze of the Ruminants, in 
that they contain inextricably mixed up in their mass, as a well-injected specimen will 
always show, maternal elements which the apparently similar Ruminant structures 
do not’. In its early attainment of the faculty of self-help, however, in the inguinal 
position, and in the small number of its mammz, the Guinea Pig presents points of 
real resemblance to the Ruminants and also to most other non-deciduate mammals. 
Secondly, Professor Owen, in the Linnean Society’s ‘ Proceedings,’* says of the 
deciduous portion of the Rat’s placenta, that it ‘‘ consists of foetal parts exclusively ;”’ 
and that the “structure of the discoid placenta in the Pteropus, like that of the Rat, 
more resembles that of the foetal portion of the cotyledon in the Cow than that of the 
cellulo-vascular, spongy placenta of the Quadrumana.” To this it must be replied that 
specimens, such as most museums possess, of uteri containing foetuses in which both 
foetal and maternal vessels have been injected show distinctly that this resemblance 
does not exist. It is impossible to inject the uterine vessels of any deciduate mammal, 
at any but the very earliest stages of pregnancy, without leaving much of the injection 
inextricably interfused with the foetal villi, whereas it is perfectly possible to do this 
with the Ruminant placentule 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 disk by which the foetal placenta is attached to the womb’’’; but it is 
difficult to see how by this peculiarity they come to resemble ‘‘ the fcetal portion of the 
colytedon 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 supporting them 
interblended organically with the foetal upgrowths. This can be shown in the Rumi- 
nants. The delicate arborescent appearance 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 Linnzus, this placental peculiarity brings them, as Linnzeus did 
bring them, into the same class as the Primates—the necessary preliminary for the 
* Tt should be borne in mind that, though in the pregnant uteri of these prolific animals the sites of former 
placentze are recognizable as well as the functional structures, the sites of the two hardly ever coincide. Reichert 
says that he has only once seen the new placenta attach itself to the place occupied by its predecessor (J. c. p. 130). 
Matters are altogether different in the Ruminants. 
* L.c. p. 16, note. See also Phil. Trans. for 1857, p. 351. § Phil. Trans. for 1857, p. 351. 
