2 66 LIGHT AND THE BEHAVIOR OF ORGANISMS 



Adams (1903) In Allolobophora foetida, by Parker (1902, 

 p. 119) in Labidocera, by Yerkes (1902) in Gonionemus, by 

 Groom and Loeb (1890, p. 169) in nauplii of Balanus, by 

 Loeb (1905, p. 276) in Polygordius larvae,^ by Hadley (1908) 



1 In an address published after this part of the manuscript was finished 

 Loeb says (1909, p. 34) that if organisms are positive in a given Kght inten- 

 sity they are positive in every intensity to which they respond at all, and 

 that forced suggestions in connection with the theory of natural selection 

 are responsible for the idea that they aggregate in the intensity of light 

 best suited for their general welfare. ''Man hat nun auch versucht, zu 

 zeigen, dass die Organismen eine 'Lichtstimmung' besitzen und ihren 

 Hehotropismus so regulieren, dass sie stets in diejenige Lichtintensitat 

 kommen, welche fiir ihr Gedeihen am besten geeignet ist. Ich glaube, dass 

 es sich hier ebenfalls um eine den Forschern durch die extreme Zuchtwahl- 

 theorie aufgezwungene Suggestion handelt. Ich habe an einer grossen Zahl 

 von Organismen Versuche angestellt, aber ich habe bei klarer Anordnung 

 der physikalischen Versuchsbedingungen auch niemals eine einzige Erschei- 

 nung gefunden, welche fiir eine derartige Anpassung spricht. Es hat sich 

 stets herausgestellt, dass positiv heliotropische Tiere gegen Licht jeder 

 Intensitat, sobald nur die Reizschwelle iiberstiegen wird, positiv helio- 

 tropisch sind. . . , Eine 'Auswahl ' einer passenden Beleuchtungsintensitat 

 habe ich nie beobachtet." 



I am unable to understand how anyone can accept the statements quoted 

 above in the face of the numerous records to the contrary; nor can I reconcile 

 these statements with those of Loeb in earlier publications. He says (1905, 

 p. 272), "Groom and I described some observations at Naples on the be- 

 havior of the naupHi of Balanus perforatus, and certain other marine animals, 

 which were at times negatively heliotropic, and at other times positively 

 hehotropic. We found that the intensity of the light determines the sense 

 of hehotropism in these animals. Above a certain intensity light makes 

 these animals negatively heliotropic, and this the more quickly the greater 

 the intensity of the Hght. By lamphght the animals were always positively 

 heliotropic." (p. 276), "The heliotropism of Polygordius larvae can also 

 be influenced by Hght. This influence consists chiefly in the fact that direct 

 sunlight makes positively heliotropic animals negative. I did not succeed 

 in making negatively heliotropic larvae positive by exposing them to weak 

 light." The idea that these larvae do not become positive in weak Hght 

 is however not supported by Loeb's observations as recorded in the same 

 paper a few paragraphs farther on. Referring to Polygordius larvae which 

 had become negative in direct sunlight he says (p. 277), "When later I 

 carried the animals back into the north room and kept the temperature 

 constant at i5°-i6° C, they again became positively hehotropic in the course 



