404 T. Bland on the Geographical Distribution of Mollusca. 
ral mode of living, and the preservation of their species ; and that 
the same species may have originated in different unconnected 
parts of the more extensive circle of their distribution.”—p. 192. 
Professor Agassiz enters upon the same subject in an article in 
the July number of the Christian Examiner, to which we also 
refer our readers. 
Prof. Adams states in his Contributions, No. 6, the conclusions 
at which he had arrived from a careful study of the land shells 
of Jamaica. 
“The distribution of the terrestrial Mollusks in Jamaica, (an 
probably of all Mollusks in all parts of the world,) is most easily 
accounted for by the following hypothesis:—that the introduc- 
tion of the existing races was effected by the creation of many 
individuals, and that they were modelled after certain, types, 
which were mostly local, and between which there existed, as at 
the present day, unequal differences, from those which merely 
distinguish individuals, to those of varieties, of species, of groups 
of species, of genera,” &c. The author subsequently observes, 
“of course the doctrine of contemporaneous origin must have a 
geological latitude.” 
We add 
occasional intermingling in one locality of varieties, which differ 
from each other as much as those which occupy distinct regions. 
then we assume the original independent creation of all the 
varieties, each originally represented by at least several individu- 
als, the facts of distribution become explicable with the greatest 
facility. The same statements might be made respecting entre 
species, and even groups of species and genera. Some are very 
others, more widely distributed, occupy the ground 
several local species. We have then indistinct satan distinct 
eseligne cbintcemecie: els penins. ahaa es Se) 
ypes, d ) % 
a 
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