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Show 110 ON CLASSJFICA'l'ION. villi ar gathered into bunches, or cotyledon , which in tho Sheep (Fjg. 45) are convex, and are received into cups of tho 1nucous membrane of the uterus; while in the Cow, on tho contrary, they are concave, and fit upon corresponding convexities of the nterus (Fjas. 44 and 46). Fig. 46. Fig. 46.-A fretal cotyledon, (}2, h~lf separated from t.he maternal cotylerlon, Cl, of a Cow. Cit, chonon. U, uterus (aft r Colin). . No one, probably, would b inclin d t o~ject to the associ a· tion of the orders just 1nentioned into one great divi ion of the Monodelphia, characteri ed by its I la. ental tructure. But ·uch grouping leaves several important points for discussion. Tho El phant, as Profe sor Ow n *has shown, has a zonary placenta, and the genus Hyram has b en known incc th time of IIomo to Le in like case. Hen , a the el phants are commonly aup· posed to be clos ly alli d with the Pachyderrnata, which possess ~iffuse, n~n-deciduate placentro, and as Hyrax i · now generally, 1f not umversally, admitted into the ame order as the I-Iorse, which has a diffus , non-d ciduat pia · nta, it is argued that placental characters d not indicate natural affinities. A question, indeed, arises, which has not been answered by those who have described the plac ntre of Elephas and IIyraw. Is the placenta of these ani1nals si1nply a zone-lilr arrangement of villi * "Description of the F tal l\1 mbnmes nnd Plncenta of the Elepl1ant." Philosophical Transactions, 1857. 'l'TIE PLAOEN'l'.lE OF 'THE ]1~DEN'l'ATA. ] ] l or cotyl don , in conn ction with whi h no d eidna i cl velop 'd, or is it a true d cidnato placenta, r , 1nblina that of the 0a1'nivora in the c s ntials of its int rnal struetur as in it. ~ t rnnl fonn? Hecent investigation has convinced 1110, that, in both these animals, the placenta is as truly deciduate a that of a Rodent; so that most unquestionably, if the pla enta] m thocl of cla sificatiou is to be adopted, both Elephas and Hyra.v mu.·t o·o into the same primary clivi ion of 1 he Monodelphia as th Rodentia and Carnivora. But do these facts really pre cnt obstacles to the placental , ystcm of classification? So far as the ca e of the Elephants is concerned, I must confess that I see no difficulty in the way of an arrangement whi l1 unites the Proboscidea n1ore closely with the Rodentia than with the Artiodactyla and Perissodactyla, the singular tics which unit the Elephants with the Hodents having been a matter of common remark since the days of Cuvier. In the absence of any definite knowledge of the placental structure of Rhinoceros and Tapirus, * it would, perhaps, b prcnlatnrc to discuss the position of I-Iyraw, as detennined by it. placenta; but if it should eventually appear, as is very probaLle, that Rhinoceros, like Tapirus and Equ~J,S, has a diffuse, non-d ~cidnatc placenta, I should have no hesitation in regarding Hyram as the type of a distinct order of deciduate Monodclphons Mammalia. Hyram, in fact, hangs by Rhinoce?''OS mainly Ly tho pattern of its n1olar teeth,-a character which affords anything bnt a safe guide to affinity in many case .. t Concerning the placentation of the Sirenia we have no in-fonnation. Among the Edentata, the Sloths have presented a cotyledonary placenta, and the Armadillos have been affirmed to possess a discoidal one. I am not aware that the minute structure of the plac nta has been examined in either of these groups, but I am * Homo's description of tho frotal membranes of the •rnpir is very poor, but Bauer's beautiful figures show clearly that the villi arc diffus , as in th Horl:le. t So(', in reference to this point, the late Professor A. Wagner 's xc lJ cnt rcmurks on Cuvier's exaggeration of the Rhinocorotic affinities of Ilymx, in • chrober's "Saugethiere." Supp. Band, Abtb. iv. p. 307. |
