52 



The Mechanistic Conception of Life 



the harbor at Kiel, when brought into the Ught and removed 

 from the mud shows positive heUotropism. It is, therefore, 

 just as incorrect to assert that the hehotropic reactions are 



governed by the bio- 

 ^ ' logical interests of the 

 animal as that this is 

 true for galvanotrop- 

 ism. We must, there- 

 fore, free ourselves at 

 once from the over- 

 valuation of natural 

 selection and accept 

 the consequences of 

 Mendel's theory of 

 heredity, according 

 to which the animal 

 is to be looked upon 

 as an aggregate of in- 

 dependent hereditary 

 qualities. 



VII 



The attempt has 

 been made to prove 

 that organisms are 

 attuned to a certain 

 intensity of light and 

 so regulate their 

 heliotropism that they 

 invariably reach that intensity of light which is best suited 

 to their well-being. I believe that this is also a suggestion 

 forced upon the investigators by the extreme application 

 of the theor}' of natural selection. I have made experi- 

 ments upon a large number of animals, but, with a clear 



Fig. 21. — Arrangement to prove that posi- 

 tively hello tropic animals move toward the source 

 of light even if by so doing they go from the sim- 

 light into the shade. W W is & window through 

 which smihght S falls into the room. By a piece 

 of board d e the sunlight 5 is prevented from 

 striking the region 6 c of a table near the window 

 and this part of the table is in the shade. Only the 

 dayUght D can reach this part of the table. 



A test-tube a c is put on this table at right 

 angles to the plane of the window. At the be- 

 ginning of the experiment the animals (e.g., the 

 winged aphides) are all at a. The animals move 

 at once toward the window, but instead of remain- 

 ing at b they keep on moving from the direct 

 svmhght into the shade toward the sovu"ce of light 

 until they all reach the end of the tube c near the 

 window (in the shade) where they remain perma- 

 nently. 



