206 
OJr THE aEOaRAPHICAL 
do not seem to inhalbit a great extent of territory ; sncli 
is the Xenodon Michaelis of Spain, the Psammophis 
Dahlii of Dalmatia, which is also found in Greece, and 
which approaches, by its slender form, to the tree-snakes ; 
the Dipsas fallax of the same countries, which should be 
considered as an anomalous species of the genus ; lastly, 
the Tortrix eryx, which only occurs in Greece, and of 
which the deserts of Africa and of Asia are the true na- 
tive regions. In comparing the observations which the 
other animals of Europe furnish, with those which we 
have announced on the reptiles of this part of the world, 
we may deduce some analogies. We see that the animals 
of the northern regions are often replaced in the centre 
of Europe by others which form local varieties, or some- 
times even races ; and the comparison of the animals of 
central Europe, with those of its southern regions, often 
presents similar results. We may cite numerous facts 
to support this opinion ; and I shall state a few. Our 
Haven is replaced in the Feroe Isles, by a variety with 
a mixture of black and white feathers. The Hooded 
Crow, and the Black Crow, are two races of the same 
genus which represent each other mutually ; the first be- 
longs to the northern parts of Europe. It is well known 
that the same thing holds vfith respect to the Sturnus 
volgaris, and S. unicolor ; the last of which, more espe- 
cially, inhabits the south of Europe. Our Emberiza 
schoeniculus is replaced, in Dalmatia and in Italy, by the 
Emberiza palustris, which has ordinarily a much stronger 
bill ; but its existence as a distinct species cannot be 
proved, because we often find individuals exactly inter- 
mediate between the two races. Everybody knows the 
local races which our Sparrow produces among the Alps 
^ We must uot imagine that each of these races is, in relation to the 
place of habitation, perfectly separated from the race which it replaces ; 
very often they mingle in their migrations, or live in the same places, 
disappearing insensibly as their representatives increase ; it happens, 
also, that individuals of the two races propagate together, as happens 
with the Corvus cornix and C. corone — a fact which I have ascer- 
tained by numerous observations, made in the neighbourhood of Dres- 
den. Consult, on these questions, the excellent vforks of M. Gloger of 
Breslau. 
