274 LAWS OF ANIMAL DISPERSION. 
Chapter LL, 
ON THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS IN GENERAL, 
AND PARTICULARLY THE CEOGRAPHY OF THE 
ANIMALS OF SOUTH DEVON. 
Great exertions have been made in every de- 
partment of science to determine principles and 
ascertain laws. The successful prosecution of this 
subject must depend in a great measure upon 
acquaintance with detail ; and since this species of 
knowledge has recently received great accessions, 
philosophers have been guided by a reasonable 
hope that a renewed inquiry after principles would 
be attended with proportionably important results. 
It is to be feared however, that the difficulties of 
the investigation have been very often insuperable, 
and have hitherto prevented us from acquiring any 
satisfactory knowledge, particularly as concerns the 
geographical distribution of animals. Indeed, as to 
primary or first causes, the reasons of the institution 
of laws, or of the occurrence of facts in connexion 
with this interesting subject, we know absolutely 
nothing. It has been customary until very lately, 
to confound together primary or general laws and 
secondary or partial laws. By primary laws, I un- 
derstand those ordinances constituting the plan, 
system, or method, according to which the whole 
