1863. | Notes on the Indian terrestrial Gasteropoda. 357 
The widely diffused species are not individually so numerous as to 
favour the idea of their extended range being the result of a vivacious 
debacle of individuals overflowing from the cradle of their species: 
indeed most of the more restricted species are fully as numerous or 
more so within their own area, than those whose area is one hundred 
times larger: we must, therefore, I think, reject the idea of their diffu- 
sion being either the result of accidental transmission, vagabond in- 
stincts, or numerical pressure of individuals. Some of the suggested 
methods indeed of explaining the subject, do not seem greatly to 
differ in kind or credibility from the nursery machinery of the blue 
bag and the parsley bed, with which crones are wont to satisfy the 
curiosity of troublesome juveniles, regarding the antecedents of the 
little stranger who is occasionally incorporated in the family circle. 
The whole question in fact of the distribution of animals hinges on 
the origin of species, anything throwing light on one, helping equal- 
ly to elucidate the other, and here my own views differ from those of 
my friends, the Messrs. Blanford. If it can be established that all ani- 
mals are descended froma single pair, whose descendants radiate from 
their own little Ararat and that the world was replenished with life from 
a point, then all the fine arguments that can be adduced against the 
feats of navigation and travel, performed by these tiny sailors under 
trying circumstances, fall to the ground before the plain deduction, 
that however the deed was accomplished, accomplished it has been; 
but till the fact is established, or unless we shackle ourselves by an 
assumption, known facts seem to favour the idea of a plurality of arche- 
typal pairs, and their sporadic distribution, (as the ethnic centres of 
the human races,) over the specific area, proportionately to its extent. 
Ample room would still be left under this supposition, for extensive 
migration of the animals themselves, and for the enlargement or con- 
traction of their area, even to the entire change of its original site, 
under pressure of changed conditions and such surface revolutions as 
many species must have been subjected to. Such changes, however, of 
distribution must have ever constituted the exception, and are probab- 
ly confined to a few, and those few widely spread species ; and to ap- 
ply the argument in favour of all, that may be admissible with a few, 
appears rather opposed to, than supported by, the most liberal inter- 
pretation of facts. The inherent weak point in the theory of the 
distribution of species, is the same as the weakest point of the Ori- 
