in Zoology and Botany. 19] 
In order to show that the views here maintained are not 
chimerical, I will here present one or two sketch-maps of dif- 
ferent families of birds, though I am well aware that our 
knowledge of natural history is as yet far too imperfect to 
pretend to accuracy*. Such sketches as these can be com- 
pared only to the rude efforts at map-making made by the 
ancients, of which the Peutinger Table is an example; and it 
is probably reserved for a distant age to introduce that degree 
of exactness into natural history which in modern geography 
is attained by a trigonometrical survey. For the sake of sim- 
plicity, in making these sketches I have omitted the consi- 
deration of species, but assuming that the genera of modern 
authors consist solely of closely allied species, I have proceeded 
to group them in what appeared to be their true position in 
respect of their affinities. In order to place these groups at 
their true distances, it is necessary to form a scale of degrees 
of affinity, to which the intervals between each genus shall 
correspond. [am aware that this scale must be, in some mea- 
sure, arbitrary ; but for this there is noremedy. The division 
of the fixed stars into seven magnitudes is arbitrary also, yet 
it is found in practice to answer the purpose. It is evident, 
from the complex ramifications assumed by the natural system, 
that it is impossible, in a zoological work, to describe each 
genus or species in the exact order of their affinities, but that 
leaps must often be made from one part of the system to an- 
other, just as in a geographical work we cannot describe the 
counties of Great Britain in their exact order of position, but 
must continually make lateral digressions, and then return to 
the main line of our route. So in anatomy, we not only can- 
not study or describe the several parts in the order in which 
they join each other in the human body, but each part must 
even be dissected out from the rest, and removed from its na- 
tural position, before we can comprehend its characters and 
functions. This is an inconvenience inseparable from the na- 
ture of the case, and it is therefore no just complaint to make 
against a systematic work, that it frequently makes diversions 
which break the order of affinities. We are therefore at liberty 
to consult our own convenience, and consequently, whatever 
may be the form which the natural system, on further survey, 
may assume, there will be no reason for departing widely from 
the usual custom of commencing with Mammalia, and pro- 
ceeding through Birds, Reptiles, and Fish, to the Mollusca, 
Annulosa, Radiata, &c. Let it not then be objected to the 
* See Plate VIII., which exhibits one of these attempts at zoological 
map-making. 
