33 
SYSTEM OF NATURE. 
monotremes, in which this hatching organ is placed with¬ 
out the body, vanishing totally in the latter group, the 
animals of which lay eggs and hatch them ; and finally, a 
third class, birds, in which this property, which is irregular 
and limited in the monotremes, becomes fully normal.”* 
It may perhaps, in this place, be as well to add that 
DeBlainville and Bonaparte have expressed their opinion 
that the placental and marsupial animals form separate, 
distinct, and equal groups; and that Professor Owen, 
under the article “ Marsupialia,” in the c Cyclopaedia of 
Anatomy and Physiology,’ after entering fully into the inves¬ 
tigation of those peculiarities wherein they differ from the 
placental quadrupeds, concludes his treatise with the follow¬ 
ing words : — “ These coincidences in the Marsupialia of 
important organic modifications of the dental, locomotive, 
vascular, cerebral and reproductive systems, establish the 
fact that they constitute, with the Monotremes, a natural 
group, inferior on the whole in organization to the Placen¬ 
tal Mammalia.”f Cuvier also says that the marsupials 
“ form a distinct class parallel to that of ordinary quadru¬ 
peds, and divisible into similar orders.”—C. R. A. 
Now, without giving the slightest colouring to the opin¬ 
ions cited above, it is evident that Cuvier, Owen, Water- 
house, Agardh and Ogilby, have clearly demonstrated the 
impropriety of mixing up the marsupial with the placen¬ 
tal animals. These authors have proved, beyond dispute, 
that the generation, brain and arterial circulation of the 
two groups is widely and radically different; that in all 
these characters the marsupials manifestly approach the 
* Mag. Nat. Hist. n. s. iii. 346. 
f Cyclop, of Anat. and Physiol, p. 329. 
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