MOTOR RESPONSES IN INVERTEBRATES 613 



alternate stripes which varied in color and in luminous intensity, but he 

 did not obtain very definite results. 



Hecht and Wolf (94), Wolf (226 to 229), Clark (35a), Wolf and Crozier 

 (231), and Hecht and Wald (93) perfected the method and obtained very 

 precise results in observations on the responses of bees, the fiddler crab, 

 and the fruit fly, Drosophila, to movement of a background contahiing 

 alternate dark and light stripes which differed in width, in luminous 

 intensity and in relative luminous intensity. They reached the follow- 

 ing conclusions: 



Under optimal conditions, the power to discriminate between surfaces 

 which differ only in luminous intensity is about 20 times as great in man 

 as it is in the honey bee and about 150 times as great in man as it is in 

 Drosophila. The visual acuity is about 10 times as high in man as it is 

 in the honey bee and about 1000 times as high as it is in Drosophila. 

 Visual acuity increases with increase in luminous intensity in such a way 

 that when it is plotted against the logarithm of the intensity, sigmoid 

 curves are produced which are practically the same in form for the three 

 species studied. It is postulated that visual acuity varies directly with 

 the number of ommatidia that are stimulated, that the sensitivity of the 

 ommatidia varies, and that the number stimulated increases as the 

 intensity increases. This accounts for increase in acuity with increase 

 in intensity, but since maximum intensity discrimination still increases 

 with increase in intensity, after acuity has become constant, it does not 

 account for this. It is therefore concluded that intensity discrimination 

 is probably correlated with frequency of impulses in the optic nerves, 

 which is in turn correlated with intensity. 



REFERENCES 



This bibliography is fairly complete for the years 1926 to 1933, inclusive. For 

 the preceding period it contains only the references cited. Extensive lists of refer- 

 ences covering different portions of this period can be found in Mast (140), Loeb (127), 

 and Rose (190). 



1. Adams, G. P. On the negative and positive phototropism of the earthworm 

 Allolobophora foetida (Sav.) as determined by light of different intensities. 

 Amer. Jour. Physiol. 9 : 26-34. 1903. 



2. Adrian, E. D., and R. Matthews. The action of light on the eye. Parts 

 I-III. Jour. Physiol. 63, 64, 65: 1927-1928. 



3. Alverdes, F. Stato-, Photo- und Tangoreaktionen bei zwei Garneelenarten. 

 Zeitsch. Vergl. Physiol. 4: 699-765. 1926. 



4. Alverdes, F. Lichtsinn, Gleichgewichtsinn, Tastsinn und ihre Interferenzen 

 bei Garneelen. Zeitsch. Wiss. Zool. 132 : 135-170. 1928. 



5. Alverdes, F. Tierpsychologische Analyse der intracentralen Vorgilnge, welche 

 bei decapoden Krebsen die locomotorischen Reaktionen auf Helligkeit und 

 Dunkelheit bestimmen. Zeitsch. Wiss. Zool. 137: 403-475. 1930. 



6. Ameln, p. Der Lichtsinn von Nereis diversicolor O. F. Miiller. Zool. Jahrb. 

 47:685-722. 1930. 



7. Andrews, E. A. Compound eyes of annelids. Jour. Morph. 5: 271-299. 

 1891. 



