544 
ZOOLOGY: H. G. MAY 
Summary. — The paper gives some new quantitative experiments 
proving that the 'instinctive' motions of animals to light are phenomena 
of automatic orientation (heliotropism) and a function of the constant 
intensity of light ; the exact expression of the function being the Bunsen- 
Roscoe law of photochemical action. 
^ Loeb, J., Sitzber. Wiirzburger physik-med. Ges., 1888; Der Heliotropismus der Tiere 
und seine Uhereinstimmung mil dem Heliotropismus der Pflanzen. Wiirzburg, 1890. Studies 
in General Physiology, 1, 1906. 
2Loeb, J., Arch. ges. Physiol., Bonn, 56, 1897, (439); /. Exp. Zool., Wistar Inst., 
Philadelphia, 4, 1907, (151); The Mechanistic Conception of Life, Chicago, 1912, pp. 27, 41. 
3 Loeb, J., and Ewald, W. F., Zentrabl. Physiol., Wien., 17, 1914, (1165). 
4 Loeb, J., and Wasteneys, H., /., Exp. ZooL, Wistar Inst., Philadelphia, 22, 1917, (187). 
5 Ewald, W. F.. Science, New York, 38, 1913, (236). 
6 Patten, B. M., /. Exp. Zool., Wistar Inst., Philadelphia 17, 1914, (213); Amer. J. 
Physiol., 38 1915, (313). 
7 Patten, B. M., J. Exp. Zool., Wistar Inst., Philadelphia, 17, 1914, (270). 
8 Groom, T. T., and Loeb, J., Biol. Centrbl., 10, 1890, (161). 
9 Parker, G. H., and Patten, B. M., Amer. J. Physiol., 31, 1912-13, (22); Abney, W. de 
W., Report 59th Meeting, British Assoc. Adv. Sc., 1899, (481); Treatise on photography, 10th 
ed. London, 1907; Englisch, E., Arch. wiss. Phot., Halle, 1, 1899, (117). 
THE APPEARANCE OF REVERSE MUTATIONS IN THE BAR-EYED 
RACE OF DROSOPHILA UNDER EXPERIMENTAL CONTROL 
By H. G. May 
DEPARTMENT OF ZOOLOGY. UNIVERSITY OF ILLINOIS 
Communicated by T. H. Morgan, July 10, 1917 
During some experiments in selection for higher and lower facet 
numbers in the bar-eyed race of Drosophila ampelophila I obtained 
six full-eyed males and five heterozygous females from the stock 
bottles and the selected lines. 
In appearance these flies could not be distinguished from normal 
full-eyed males and heterozygous females. Three males and three 
females were mated with bar-eyed flies and gave the offspring antici- 
pated from such normal flies. In two cases the males gave only bar- 
eyed male offspring and heterozygous female offspring. In the third 
case the offspring were not examined until twenty-four days after the 
mating had been made and as the result of the hatching of individuals 
from the second generation bar-eyed females and full-eyed males were 
also present. The offspring of the heterozygous females in each case 
consisted of bar-eyed and full-eyed males and bar-eyed and heterozygous 
females. Some of the offspring of a full-eyed male were interbred and 
produced full-eyed males and bar-eyed females as well as bar-eyed males 
