24 Trans. Acad. Sci. of St. Louis 



always moves parallel to a wall and not at right angles 

 to it. 



Watch the behavior of tent caterpillars. They move 

 upward and outward, feeding when they find the proper 

 materials. Later, satiated, they return to the tent, 

 "Negative geotropism when hungry, positive geotropism 

 when satiated", some say. Or, take the recessional cater- 

 pillars. They move along in a procession with the head 

 of one in contact with the larva just in front of it. Lead 

 them to the rim of a bucket and start the procession 

 around the rim. When the circuit has been completed, 

 knock aside the superfluous caterpillars and permit the 

 head of the leader to come in contact with the tip of the 

 abdomen of the last member of the procession. They 

 will continue to march around the rim hour after hour.^ 

 ''Positive thigmotropism", you say. Let us analyze the 

 behavior of such caterpillars. Arrange a vertical maze 

 consisting of an upright about one-inch in diameter to 

 which are attached a number of jointed arms. Let the 

 arms be so articulated that they can be bent in a variety 

 of ways. Such a maze contains no succulent buds nor 

 tender leaves for the larvae to nibble; hence there can 

 be no reversal of tropism due to satiety. A caterpillar, 

 when placed at the foot of such a maze will explore it. It 

 may continue up to the center support to, the top or it 

 may explore one or more of the arms. After a time it is 

 almost certain to descend the maze to the ground. This 

 behavior may be repeated several times. The apparatus 

 may be so manipulated that the caterpillar crosses the 

 light at Hev(;ral different angles, so that it moves toward 

 the wind, from the wind, and at angles to it, and so tliat it 

 moves at times toward the earth and at other times away 



'Fabre, J. H.; The Life of the Caterpillar, Translated by Alexander 

 Teixeira de Mattos. Dodd, Mead & Co., 1916, |)i>. 58-88. 



