98 



I have given at the outset the proluible cause-i whicli liave liroujflit a'luiit the 

 great differences between the Pacitic slope tishes. 



We mu8t look to other causes for the great variation between sijiecies of un- 

 doubted Atlantic origin and esi>ecially the variation in the same species, which 

 reaches its culaiiuation in Lmciscmi l)alteatu~<i an<l Ayosia nubila. The climatic, 

 ahitudinal and geological differences in the different streams and even in the 

 length of the same stream are very great on the Pacific slope. To these different 

 environments we must attribute the ccmditions set forth in the present paper for 

 Lcm-.is'Jus balteatttg. These differences in different localities in the same stream can 

 only become estahlished in non-migratory species. No such differences are iu be 

 expected for a migratory species. Isolation for the sjiecimens of any locality when 

 free intermigration is possible, seems strange. .\n analogous condition is to be 

 found on the Galapagoes Islands. I>r. Kanr tells me that islands within plain 

 sight of each other harljor distinct varieties of the same sjtecie- of Idrd^ which 

 could readily intermigrate, but do not. 



This raises the (juestion of the sort of intluence exerted by the environment. 

 t> it merely selective, or is it directive? Is the variation promiscuous and in- 

 herent in the species, or is it determinate and forced in certain directions by the 

 environments? The latter seems to me the better way of reading such condition« 

 as are represented by the many curves which show a greater variation towards an 

 increased number of rays than towards a decrease of rays. Here the variation is 

 tiot jiromiscuous, Init detinitely determinate, ."^ee. in this connection, the <rurve 

 tor all the sjtecimens. 



The origin of new varieties is admirably illustrated by the curves for Lake 

 VVashington and Umatilla. In these, two distinct j»eaks are found. While no 

 varietal value is claimed for these peaks, isolation of members of such peaks, either 

 |ihysi(dogically or locally, woubl tend to establish such incipient varieties as 

 species, 



EXPi.ANATlON OF FI«rKES>. 



the vertical lines in all cases stand lor a delinite number «\ aTial ray>. The 

 total height of the figures represents 100 ])er cent., and the height of the curves at 

 ^ny point, the per cent, of specimens having the i>articular number of rays in 

 (he anal. 



V'\ix. 1. Curve of variation for 217 s])ecimens of Leucueus hi/drophhx from the 

 upper .'<nake, and 825 specimens of LeuciscusbaUeatus from many local- 

 ities, ranging from 1 to over 5,000 feet. The two series of speci- 

 mens are combined in the l)roken line curve. 



