Animal Geography. 
49 
1877.] 
have before us a distinction of the highest order. But here 
is a fresh difficulty : it is only Australia which offers us so 
sharp a demarcation, and even this extends merely to the 
Mammalia : its birds and insects, though very distinct, not 
being separated from those of other parts of the world by 
so broad a boundary line. In separating region from region 
we cannot always avail ourselves of characteristics abso- 
lutely equal in value. This, as we shall afterwards see, has 
led some systematists to maintain that Australia and South 
America are marked off from each other and from the rest 
of the world by features more striking than those presented 
by any other region. We must therefore call in another 
principle, already shadowed forth in the admission that 
mere poverty of species cannot constitute a zoological 
region. We must take into consideration richness and 
variety of forms, as well as speciality. Nor must we insist 
upon being able to prove that all our primary divisions are 
of precisely equal rank. Nature will not adapt itself to our 
systematic classifications, whether geographical or morpho- 
logical. Look, e.g. f at our use of the term “ order.” It is 
applied equally to two such groups as Carnivora and Marsu- 
pialia. It must be admitted that the latter comprises at 
least four groups which, if more developed, might claim to 
rank as distinct orders. Or let us look at that vast assem- 
blage of animated beings known as the “ order ” Coleoptera, 
but containing carnivorous, omnivorous, frugivorous, and 
lignivorous groups, differing widely as well in structure as 
in habits. Were they bulkier creatures, would not the 
“ stirps ” Geodephaga be entitled to the position of an order 
equivalent and parallel to Carnivora ? Thus we see that 
our morphological groups, as well as our geograpical regions, 
are by no means equal in value. 
But to return : the question next arising concerns the 
foundation of our regional division. Shall it be founded 
upon the consideration of some one sub-kingdom or class, 
and, if so, upon which ? Mr. Wallace, like some of his 
predecessors, takes the Mammalia as his standard, and only 
calls to his aid the distribution of other groups to deter- 
mine* doubtful points, or by way of corroboration. We 
cannot help thinking that inserts have a higher claim to be 
selected for our guidance. They form, so to speak, the 
round numbers of the world’s animal species, all other tribes 
and classes being in comparison a mere fractional amount : 
they are rarely purposely introduced by man into foreign 
countries, and the few which follow him parasitically, such 
VOL. vii. (n.s.) b 
