VI. 
OF ZOOLOGICAL FOCI, OR POINTS OF ORIGIN WHENCE 
GENERA AND SPECIES ARE DERIVED. 
The distribution of species, as treated of in the pre- 
ceding chapter, has thus far been considered only as 
influenced by existing causes, whose operation is known. 
These, however, will hardly account for the present con- 
dition of all the species, or rather, some of them as it 
would seem, occupy their present positions, notwithstand- 
ing the restraining influences, which, if the preceding 
views are correct, should have limited them within more 
narrow bounds. The species alluded to, are those which 
occupy different and widely distant countries and conti- 
nents, and which have already been discovered upon so 
many points of the earth's surface, as to indicate an 
almost universal diffusion. The researches which are 
now continually undertaken, to elucidate the zoology of 
almost every part of the world, frequently bring to our 
knowledge instances of the wide range of species, which 
had been noticed previously only in a single country ; 
and the number of these is already large. The most 
vol. i. 37 
