NO. lO TROPISMS OF LEPIDOPTERA — McINDOO 21 



wandered up and down, but finally went as a rule to the bottom where 

 many made cocoons in the twine, while a few dropped by threads to 

 the floor. This shows that larvae of the sixth instar at cocooning 

 time are strongly geopositive, but shortly before this they were usually 

 indifferent to gravity. The younger instars were either indifferent or 

 geonegative. Therefore, at cocooning time negative phototaxis and 

 positive geotaxis are closely correlated, and when one is known the 

 other can be correctly assumed. In a case of this kind why assume 

 the presence of geotaxis ? Instead, why not say : " They go up owing 

 to a hunger urge, and down because of a cocooning urge? " To the 

 writer it seems that they " know " up from down at all times. 



While ascending the branch a few of the larvae seemed to perceive 

 the small apple when within an inch of it. They stopped crawling 

 and reached as far as possible in the direction of the apple. These 

 and others after finally reaching it ceased to wander farther. 



IV. THIGMOTAXIS 



I. REVIEW OF LITERATURE 



Dewitz in 1885, according to Loeb (42, p. 23; 43, p. 156), first 

 called attention to a contact-irritability exhibited by spermatozoa of 

 a cockroach. Three years later Loeb noticed the same tropism in 

 Infusoria and gave the name " stereotropism " to the peculiarity, 

 which some animals have of orienting their bodies in a definite way 

 toward the surfaces of solid bodies. Since this tropism in those ani- 

 mals having tactile organs is brought about through the sense of touch, 

 the term thigmotaxis (touch arranging) seems to be more appropriate. 



Loeb (43, p. 158; 44, p. 167) believes that positive thigmotaxis is 

 second to chemotaxis in bringing about the union of the sexes. The 

 holding of the female during mating is evidently a thigmotactic sense, 

 and since only males and females of the same species mate, he believes 

 that thigmotaxis plays a part in the selection of the proper species. 

 The same author (42, pp. 22, no) found certain moths (Aviphipyra) 

 to be thigmotactic because in tests they crept into crevices and in 

 nature they remain in clefts in the bark of trees. He was able to 

 show that light in such cases was not a factor, for the insects were 

 forced to bring as much of their bodies as possible in contact with 

 solid bodies. The friction and pressure produced by the solid bodies 

 are considered by him to be the cause. 



Dewitz (9) says that thigmotaxis is widely distributed among the 

 lower animals and that the mode of living and conduct of many species 

 can be traced back to it. Insects fasten their bodies tightly to promi- 



