A Hit-or-Miss Universe 



329 



test-tube in a room, they all crawl 

 toward the window, or toward a lamp; 

 the animal is positively heliotropic. 

 It is this positive heliotropism which 

 makes them move upward where they 

 find their food, when the mild air of 

 the spring calls them forth from their 

 nest. At the top of the branch, they 

 come in contact with a leaf, and chem- 

 ical or tactile influences set the man- 

 dibles of the young caterpillar into 

 activity. If we put these larvae into 

 closed test-tubes which lie with their 

 longitudinal axes at right angles to a 

 window, they will all migrate to the 

 window end, where they stay and 

 starve, even if their favorite leaves are 

 close behind them. They are slaves 

 of the light. 



"The few young leaves on top of a 

 twig are quickly eaten by the caterpillai . 

 The light, which saved its life by making 

 it creep upward where it finds food, 

 would cause it to starve could it not 

 free itself from the bondage of positive 

 heliotropism. The animal, after having 

 eaten, is no longer a slave of the light, 

 but can and does creep downward. It 

 can be shown that a caterpillar, after 

 having fed, loses its positive helio- 

 tropism almost completely and per- 

 manently. If we submit unfed and 

 fed caterpillars of the same nest con- 

 tained in two difTerent test-tubes to the 

 same artificial or natural source of 

 light, the unfed will creep to the light 

 and stay there until they die, while 

 those that have eaten will pay little 

 or no attention to the light. Their 

 sensitiveness to light has disappeared; 

 after having eaten they become inde- 

 pendent of light and can creep in any 

 direction. The restlessness which ac- 

 companies the condition of hunger 

 makes the animal creep downward — 

 which is the only direction open to it — 

 where it finds new young leaves on 

 which it can feed. The wonderful 

 hereditary instinct, upon which the life 

 of the animal depends, is its positive 

 heliotropism in its unfed condition 

 and its loss of this riehotropism after 

 having eaten." 



There is no room for mysticism in 

 explanation of this tropism, because it 

 ■can be imitated artificially, as in a 



wooden "dog" with eyes of seleniiun, 

 which John Hays Hammond, Jr., manu- 

 factured several years ago. This was 

 mounted on wheels, and the action of 

 light on the selenium influenced motors 

 attached to these wheels. The "dog' 

 would, therefore, follow a man with a 

 lantern, even if the man walked in 

 circles or zigzags. It is certain that 

 the heliotropism of the animals above 

 described is of a similar character, 

 sensiti^'e areas in the eyes or on the 

 surface of the body being stimulated 

 by light and communicating an impulse 

 to the muscles, directly or indirectly. 



If in several critical cases the existence 

 of highly specialized instincts can be 

 explained on a purely mechanical basis, 

 as above, Dr. Loeb thinks it unscientific 

 to bring in mystical influences, of a 

 kind not capable of investigation, to 

 account for other instincts. 



7. It is equally important, in Dr. 

 Loeb's view, to avoid any mysticism 

 in thinking about the relation of the 

 environment to the organism. The 

 very term "environment," he objects, 

 has a vagueness that is almost mystical ; 

 if instead of this the definite parts of 

 the environment, such as temperature, 

 moisture, saltiness of sea water, etc., 

 were spoken of, it would make for clearer 

 thinking. When these different ele- 

 ments of the environment are tested it is 

 found, if disturbing influences can he 

 avoided, that a living organism reacts 

 just as precisely as a thermometer. 



Again, the question of adaptation to 

 the environment leads to a lot of loose 

 thinking. It is sometimes supposed 

 that the environment can cau.se an 

 adaptive modification of the organism, 

 and that such a modification may even 

 be hereditary; but there are striking 

 cases which warn against the falseness 

 of this explanation of the origin of 

 characters. Heliotropism, for example, 

 might be supposed to be due to the 

 inheritance of the effects of light on 

 many generations of caterpillars; but 

 it is found that caterpillars which spend 

 their lives under the bark of willow 

 trees and a shellfish which spends its 

 life in the mud, are likewise heliotrooic- 

 although neither of these has ever nad, 

 so far as is known, a chance to make 



