428 



EVOLUTION AND ANIMAL LIFE 



these movements are usually more rapid and more exact than 

 with the lower forms. This is because the organs of sense 

 and action, the sense cells, nerve fibers, and muscles are all 

 highly specialized. In the starfish sensation is slight, nervous 

 communication slow, and the muscular response sluggish, but 



the method is apparently the 

 same. 



But in recent years many 

 biologists have come to believe 

 that much of the behavior of 

 the simplest animals, and some 

 of the actions of the higher, 

 are controlled in a more rigidly 

 mechanical way than the above 

 statements suggest; that, in a 

 word, much of the action, and 

 apparent instinctive or intelli- 

 gent response of animals to ex- 

 ternal conditions, is an immedi- 

 ate physicochemical rather than 

 vital phenomenon; that the 

 animal body in its relation to 

 the external world is much 

 FIG. 264. Diagram showing how the more like a passive, senseless, 



( Protozoan, .Oxytricha iallax, reacts to although Very Complex, ma- 

 cold; slide is heated at upper end and i , i n i 

 an Oxytricha beginning at 1 continues chme > Stimulated and Controlled 



to react hy turning a little to right by external factors and con- 

 and backing and advancing and re- ditlons, than like the percipient, 



peatedly turning a little to right and , . . 



backing and advancing until posi- determining, purposeful creature 



tion 1 4 is reached. (After Jennings.) that Olir USUal Conception of the 



organism makes it out to be. 



Clever experimenters, as Loeb, Lucas, R?dl, Bethe, Uexkull, 

 and numerous others, believe themselves justified in explaining 

 a host of the simpler actions or modes of behavior of animals, 

 on a thoroughly mechanical basis, as rigorous, inevitable 

 reactions to the influence or stimulus of light, heat, contact, 

 gravity, galvanism, etc. Phototropism, stereotropism, geo- 

 tropism, etc., are the names given to these phenomena of re- 

 sponse by action and behavior to stimuli of light, contact, and 

 gravity respectively. 



Some of these biologists are ready to carry their giving up 



