ADAPTATION 193 



burrow in the sand in the bottom of the river, 

 others fly with wing strokes through the air above 

 the river, and others occupy all possible spaces 

 between. In appearance they parallel our gar- 

 fish, our pickerel, our top minnows, our pom- 

 pano, our' trout, our minnows, our suckers, our 

 darters, our fresh- water herrings and shad; and 

 besides these there are a variety of shapes and 

 sizes and adaptations not to be found in other 

 fishes. Chief of these is the series ending in a 

 true flying fish, i.e. a fish with wing-like pecto- 

 rals, large muscles to move them, and the ability 

 to propel itself with wing strokes along the sur- 

 face of the water for forty or more feet, and to 

 continue its flight for five or more feet in the air. 



C. Causes of Adaptations. The causes lead- 

 ing to new adaptations may be intrinsic or ex- 

 trinsic. The theories of Nageli, Weismann, and, 

 in part, of Darwin and De Vries, are based on 

 intrinsic causes ; those of Buff on, Lamarck, Gu- 

 lick on extrinsic. 



D. Orthogenesis, Nageli, and in a modified 

 form Eimer, Waagen, Osborn, Whitman, and 

 others, have shown that lines of evolution are 

 orthogenic, predetermined in definite directions. 

 According to Nageli direction is maintained by 

 the make-up of the protoplasm of the individual. 

 According to Weismann direction is given by the 

 process of germinal selection, helped out by per- 

 sonal selection. By Osborn and others it is recog- 

 nized but not explained. 



