360 W. von BUDDENBROCK 



is lighted from one side and not from the other. Since now the 

 protoplasm of both sides is adapted to an equal amount of 

 light, the side that is least lighted is nearer to the optimum 

 strength of light. Its protoplasm is in a phototonic condition, 

 while the strongly lighted side has lost its phototonic condition. 

 Therefore the darkened muscles are in a condition to contract 

 normally, and the brightly lighted ones are relaxed. Under 

 these conditions the animal turns toward the darker side. * * *" 



' Dichtung und Wahrheit," —poetry and truth — might be 

 placed as a title above this entire statement. Truth is found 

 only in the italicized 14 first and last sentences. What lies be- 

 tween can only be admired as evidence of a richly endowed 

 imagination, it has no scientific value. We know nothing about 

 what strength of light the " protoplasm " is adapted to. Its 

 phototonic condition is completely hidden from us and conse- 

 quently also the action of light upon darkened and lighted 

 muscles. What we really know is that in and beneath the 

 epithelium of the earthworm cells are found whose structure 

 certainly indicates that they are sensitive to light, that from 

 them nerves run to the ventral nerve cord, and other nerves 

 from there to the muscle-layer of the skin, further, that the 

 whole tropism ceases if I destroy the ventral nerve cord, so 

 that we may suspect the existence of a reflex arc: epithelial 

 cells sensitive to light, sensory nerves, ventral nerve cord, motor 

 nerves, and muscle layer. Without hesitation I leave it to the 

 reader to decide which of the two possibilities, the reflex arc 

 or Davenport's assumption, is more probable. A certain possi- 

 bility remains for an explanation in Loeb's sense. Assuming 

 that the criticisms made above are unfounded, and referring 

 exclusively to those cases where no reflex arc is at present 

 demonstrable, then, from this standpoint, the tropism theory 

 is master of the situation. 



I wish here to draw attention to two tropisms of this kind 

 (with no demonstrable reflex arc) . The first concerns the reac- 

 tions to the stimuli of gravity of such animals as are known to 

 have no statocysts, especially those which still manifest geo- 

 tropism even after the removal of these organs. The second 

 concerns the growth phenomena of certain hydroid polyps which 

 result in placing the animal in the direction of the rays of light. 



14 The italics and the words (the earthworm) are the present author's. 



