REMARKS ON THE CLASSIFICATION OF MAMMALIA. 513 
remarkable lateral connections between the deviative groups themselves. 
These views I endeavoured to render clear by the aid of a diagram. 
Were I now going over the same ground I might somewhat modify 
the details, but on the whole, frequent reconsideration with the 
practical reference of plans to an extensive collection of specimens has 
confirmed me in the views I brought before you, and I have been led 
to extend their application to some other departments of Natural 
Science. Without doubt if my principle is good it will admit of very 
wide application, though there may be natural classes consisting 
entirely of a central group of families, without any considerable devia- 
tions of structure, and others formed by a circle of characteristic 
structures that might seem to have relation to some common central 
body, though none such exists, or is known to us. My object on the 
present occasion is to bring under your notice an application of the 
same principle of a typical central group, with deviations that 
admit of a circular arrangement to the class mammalia, Not to 
trouble you here with details of various systems, the Cuvierian 
arrangement of mammals as improved to correspond with the present 
state of knowledge gives us no less than twelve orders in that class :— 
ist. Bimana, for man only; 2nd. Quadrumana, monkeys and lemurs ; 
‘3rd. Cheiroptera, bats; 4th. Insectivora, moles, shrews and hedge- 
hogs; 5th. Carnivora, cats, dogs, weasels, bears, and seals; 6th. 
Cetacea, whales and dolphins; 7th. Rodentia, squirrels, rats, beavers, 
&e.; 8th. Edentata, ant-eaters and sloths; 9th. Pachydermata, 
elephants, swine, horses ; 10th. Ruminantia, antelopes, oxen, deer, &c. ; 
11th. Marsupialia, pouched animals, as opossums and kangaroos ; 
12th. Monotremata, the Hchidna and Ornithorhyncus. Respecting 
the reality of these as so many natural groups, the great question is, 
whether the lower organisation of the brain and the reproductive 
system in the marsupialia and monotremata presents the kind of 
difference that should characterise orders. The settlement of this 
question depends on what we ought to understand by orders. One 
great philosophical naturalist whose authority stands deservedly high— 
Agassiz—in the introduction to his noble work recently issued, main- 
tains that whilst “classes are natural divisions, characterised by the 
manner in which the plan of their respective great types is executed 
and by the means employed in the execution; orders are natural 
groups, founded upon the degree of complication of the structure.’ 
Degree of development should, according to this view, be the principal 
