1877.] On the Distribution of Fresh- Water Fishes. 607 
The following summary and conclusions are offered : — 
I. That the mechanical force used in locomotion during the 
struggle for existence has determined the digits which are now 
performing the pedal function in such groups as have undergone 
digital reduction. 
II. That where the distribution of mechanical strains has been 
alike upon all the digits of the manus or pes, or both, they have 
remained in a state of approximate uniformity of develop- 
ment. 
II. It is held that these views are Lamarkian and not Dar- 
Winian, that is, that they more especially take cognizance of me- 
chanical forces as mutating factors in evolution, in accordance 
with the doctrine of the correlation of forces. 
ON THE DISTRIBUTION OF FRESH-WATER FISHES. 
. BY DAVID 8. JORDAN. 2 
THE writer has been engaged during the two past summers 
(1876-1877) in collecting fishes in the upper waters of 
the different river basins in the Southern States, with a view to 
ascertaining the fish fauna of each and to throw as much light as 
possible on the laws which govern the distribution of the species. 
In 1868 and 1869, Professor Cope made very thorough explora- 
tions of the upper waters of the Cumberland, Tennessee, 
Kanawha, James, Roanoke, Neuse, Great Pedee, and Santee. In 
order to supplement Professor Cope’s work, ‘the writer, with his 
ichthyological assistants, Prof. A. W. Brayton and Mr. C. H 
‘Gilbert, began with the Santee, and proceeded westward across 
, the different river basins, including the Santee, Savannah, Oconee, 
Ocmulgee, Chattahoochee, Alabama, Tennessee, Cumberland, and 
Ohio. These rivers, as well as those examined by Professor 
Cope, have their rise in the Alleghany Mountains, from which 
they flow in different directions and under the most widely varied 
physical conditions, thus affording the most favorable oppor- 
tunity for the study of the effect of these conditions on the dis- 
tribution of fishes. 
_ Some forty-three species new to science were obtained by us 
in these Southern rivers, among them several singular and interest- 
-mg forms, but of these I do not purpose to speak at present. I 
confine myself to the statement of a number of proposi- 
tions — apparently truths — in regard to the distribution of 
