34 VICTOR E. SHELFORD. 



2. Beginning at the sources of the streams of tin- devi-lo]>- 

 menta! series considered, we find the same species represented 

 in essentially the same order in all the streams, in so far as the 

 series of conditions is present. The only species in the youngest 

 stream is the same as the species nearest the sources of the larger 

 stream-. 



3. Migration of conditions for breeding is an important cause 

 of fish migration, but fish reactions outside the breeding season 

 may lie often more important than movement of conditions 

 necessary for breeding over the route of migration. Migration 

 may even be due to reactions to a single factor. 



4. Fish entering a stream will take a position in the stream 

 suited to their ecological constitution without regard to the 

 time and mode of origin of these conditions. 



5. There is a succession of ecological types over a given point. 

 Ecological succession is based on similar mores (physiology, be- 

 havior, habits and mode of life) of fish communities as a whole 

 or comparable species of communities. 



6. Physiographic analysis locates the animal in its environ- 

 ment and is but a method of studying the organism as a whole 

 and a basis for proceeding to its analysis. 1 



VI. ACKNOWLEDGMENTS AND RIHLIOGRAPHV. 



The identification of the fish discussed in this paper are by 

 Dr. S. E. Meek and Mr. S. F. Hildebrand, and of the Mollusca 

 by Mr. F. C. Baker. Some of the seining was done in co- 

 operation with Mr. Hildebrand. Without the assistance of these 

 gentlemen this paper would not have been written. I am in- 

 debted to Professor F. R. Lillie and Mr. Ellis L. Michael for 

 criticising the manuscript. 



BIBLIOGRAPHY 



Abbott, C. C. 



'70 Notes on the Freshwater Fishes oi NV\\- Jris.-y. Amrriran .Naturalist. 1870, 



p. 99- 

 Adams, C. C. 



'OI Ka-rlrvrlini; and it- F.iunal Siniliranrr with Illustrations I'rom South- 

 K-rn I'nitcil States. AMI. Nat. XXXV., pp. 839-52. 



1 ' 'iiti iliiitii 'ii Mom tin- Hull /oolojjical l.almiatoi irs <>| the I'nivrrsity of 

 Chicago, Marino Biological Laboratory t' San Diego, February 20, K;II. 



