VARIATIONS IN REACTION TO LIGHT. 9 
diffused daylight. Under such conditions these animals, which react 
positively, did not halt at the junction of diffuse light and direct sunlight 
and turn again backwards to the stronger light, but proceeded on in the 
feebler light toward the incident point right up to the end of the tube. 
From this experiment, Loeb argues strongly against the anthropo- 
morphic point of view which would assign any choice to the animal as to 
whether it sought, or turned from, the hight because the light was pleasant 
to it or the reverse, and urges that the whole process 1s mechanical or 
automatic, the animal's head beige. turned by the stimulus irresistibly 
towards the light, and the whole movement following inevitably upon 
this turning. 
Without assuming any extravagantly anthropomorphic point of view, 
it may be maintained that the ingenious experiment scarcely supports the 
interpretation placed upon it, and that the whole matter depends upon the 
force of the stimulus outweighing the degree of development, of what 
represents the intelligence of the animal, or, if the expression is more 
suitable, the development of the nervous system, or, in more general terms 
still, the co-ordination of the organism. 
When the animal’s body or the sensitive area of it passes from the 
area of direct sunlight into the less illuminated area of diffuse daylight, 
in order to turn back into the brighter area of sunlight, the sensitive 
surface would require for a time to be turned away from even the diffuse 
light into a region of shadow from its own body, that is to say, it would 
require for the time to behave as a negatively phototactic animal, and 
reduce the intensity of illumination of the sensitive area. This supposes 
a degree of intelligence and of memory for the * pleasanter ’ (or more near 
the optimum) stimulus which the organism does not possess, and hence it 
does not turn; but a more highly organized animal would turn, and once 
more seek the stimulus which suited the organism best. 
It is such excess of stimulus over organization which makes the moth 
burn itself in the flame or the bird dash itself to pieces against the 
lighthouse lantern, and in my opinion this differs in degree of complexity 
only, but not in kind, from the strength of the irresistible impulse which 
forces the victim of any drug habit to keep on drugging himself, or leads 
