188 C. F. CURTIS RILEY 



merits, one of which was darkened and the other exposed to 

 diffuse daylight, moved toward the darkened compartment and 

 tended to collect there. According to Graber's (I.e., pp. 39, 

 40) description of his own methods used in experimentation, 

 the natural inference is that he used strong diffused daylight 

 as a source of stimulation, except in those instances where it 

 is stated specifically otherwise. The following quotation pre- 

 sents his results (I.e.): 



"Da die meisten Versuche, die ich mit diesen ekelhaften Tieren anfieng, 

 ein negatives Resultat ergaben, glaubte ich mich in eine genauere Licht- 

 gefuhl-Prufung nicht einlassen zu sollen und geh' ich auch bei der Mitteil- 

 ung der erhaltenen Reactionswerte ganz summarisch zu Werke. 



"Aus der Vergleichung von Weiss und Schwarz geht zunachst hervor, 

 dass, wie zu envarten war, die dunkle Abteilung der hellen bei weitem 



vorgezogen wird. 



Weiss 

 1) 



Schwarz 8 . 4 



"Darnach ist also die Lichtscheu der Krote (obiger Quotient beruht 

 freilich nur auf 5 aber unter sich iibereinstimmenden Beobachtungen) 

 entschieden viel grosser wie jene des Frosches (aber kleiner wie die des 

 Triton)." 



While it is evident that the results of Graber's experiments 

 differ from those of the writer, yet attention should be drawn 

 to the fact, as indicated in the first paragraph quoted, that 

 there was evidently some doubt in the author's mind as to the 

 correctness of his own results. Plateau (1889, p. 82), however, 

 working with Rana temporaria and Bufo calamata reached con- 

 clusions of an opposite nature. He demonstrated, when speci- 

 mens were liberated in an experimentation pox lighted by 

 windows at one end only, that both specimens responded posi- 

 tively to the light and jumped toward the source of illumina- 

 tion. One infers from Plateau's (I.e., p. 81) statement that 

 strong diffuse daylight was used in his experimental work with 

 amphibians. According to Loeb (1890, p. 90) frogs respond 

 negatively to strong diffuse daylight. Torelle (1903, p. 469) 

 experimented with Rana virescens virescens and Rana clamata 

 and demonstrated that both species oriented in such a manner 

 that their heads pointed toward the source of illumination, 

 diffuse daylight, and also that they moved toward the light. 

 Dickerson (I.e., p. 32) states that the frog moves toward diffused 

 light, probably meaning strong diffuse daylight. 



