824 THE EFFECTS OF CONDITIONS 



per cent, of all individuals). These differences of 

 character Heincke attributes very largely to the differ- 

 ent conditions of development. Thus, as regards the 

 Western Baltic herring, the larvae of the spring brood, 

 developing in the warm and less saline waters of the 

 Schley, reach the young herring stage within three or 

 four months. Those of the autumn brood, on the other 

 hand, which hatch in the more saline waters of the 

 open sea, need the whole winter and spring, or 7 or 8 

 months, to reach the same stage. 



The fish of the Atlantic and Pacific slopes have been 

 studied and compared by Eigenmann.* In the eight 

 families compared, the number of species on the At- 

 lantic slope was more than twice as great as on the 

 Pacific, but, nevertheless, the variation in the number 

 of fin-rays in the Pacific species was greater in all but 

 two of the families. The author considers that this 

 may be due to the fauna being of diverse origin, and to 

 its being comparatively new, and not yet in a state of 

 equilibrium. The fish Leuciscus balteatus was studied 

 in detail, and it was found that every locality in which 

 it was examined had a variety peculiar to itself. As a 

 rule, the lower the elevation of the locality from which 

 the fish were obtained, the greater the number of fin- 

 rays. The following are the mean values in support 

 of this statement: 



NUMBER OF AVERAGE 



ELEVATION. SPECIMENS EX- NUMBER OF 



AMINED. RATS. 



1750 feet, 189 18.4 



1078 2000 feet, . . . . . 234 16.6 



2001 3100 feet, 388 17.5 



5000 feet or more, 10 16.0 



* Amer. Naturalist, xxix. p. 10, 1895. 



