16 Prof. Owen on the Class Mammalia. { 
totle; the Seals and the Whales balance all the rest of the class 
in the Illigerian system. The subdivisions, also of these primary — 
groups, based exclusively on characters of locomotion, have met 
with little acceptance beyond some of the schools of Germany. 
De Blainville appears first, 1816, to have adopted a character 
from the reproductive system for the primary division of the 
Mammalia, viz. into the ‘Monodelphes,’ ‘ Didelphes,’ and ‘Orni- 
thodelphes.’ His orders are in the main a return to the Linnean — 
Pha aud nomenclature, with some peculiar views, as ¢. 9. of 
the quadrumanous or primatial affinity of the Sloths, which 
have never gained acceptance. But his system indicates a clearer 
appreciation or stronger conviction of the value of the character 
of parity and imparity in the number of toes of the Ungulata, — 
first suggested by Cuvier,* than was subsequently entertained 
by the originator of the idea. : 
The position of the marsupial and monotrematous quadrupeds — 
at the bottom of the class Mammalia, and the higher value as 
signed to the group which they constituted, than that in the 
ie 
See 
aS 
ing from all other mammads in the absence of a placenta, and of : 
the great commissure of the brain, in certain bird-like characters 
of the heart,t and from all other diphyodont Mammals in a less 
number of premolars, and a greater number of true molars,— — 
depending essentially on the retention of a milk-tooth (m. 4) 
which is displaced and changed in the placental diphyodonts,— _ 
that the true affinities of the didelphid and pomrrivar te bee mam 
mals to each other, and their true position in the class Mammalia, 
were finally recognized. 4 
n_the ‘Systema Vertebratorum,’ communicated in 1840 to 
the Linnean Society by that accomplished and indefatigable 
zoologist Prince Charles Lucien Bonaparte, the primary subdivi © 
sion of the Mammalia according to developmental and generative — 
characters is adopted; and the first diyision or series Placentalia 
is subdivided, agreeably with M. Jourdan’s distribution of Mam-_ 
malia in the Leyden Wasim, into the two subclasses Hlucabilia 
and fneducabilia, the latter including the orders Bruta, Cheirop, 
tera, Insectivora and Rodentia, with the common character of 
‘cerebrum unilobum.’ This I regard as the most important im — 
ahchig a it the classification of the Mammalia, which has — 
en proposed since the establishment of the natural character — 
of the implacental or ovo-viviparous division. —— 
* agence a ed. 1812, p. 9; tom. ii, ed. 1822, p. 72. 
+ Ont on of the Marsupialia ii, Pe 
815 (1889). supialia, Zoological Transactions, vol. il, P- 
