C*ROSSINGOVER IN DROSOPHILA 193 



in the very earliest oocytes. This is corroborated by the fact 

 that high temperature has little effect if applied to females in the 

 early larval condition. 



7. This is strong evidence that crossingover does not occur at 

 the late stage in oogenesis used by Janssens as the basis of the 

 chiasmatype, and makes it probable that it occurs at the fine 

 thread stage. The evidence also disproves the reduplication 

 hypothesis as an explanation of linkage in Drosophila. 



8. Tests of the first and third chromosomes by the same 

 methods show that high and low temperatures are ineffective 

 in causing a change in the percentage of crossingover. This is 

 further evidence of the reality of the 'genetic chromosomes.' 



LITERATURE CITED 



Bateson, W. 1913 Mendel's Principles of Heredity, 3d impression, Cambridge. 

 Baur, E. 1912 Vererbungs- unci Bastardierungsversuche mit Antirrhinum. 



II. Zeits. Abst. u. Vererb., 6. 

 Bridges, C. B. 1915 A linkage variation in Drosophila. Jour. Exp. Zool., 



vol. 19, no. 1, July. 

 Greeley, A. W. 1902 Artificial parthenogenesis in starfish produced by a 



lowering of temperature. Amer. Jour. Phys., vol. 6, p. 296. 

 Howell, W. H. 1913 Textbook of Physiology, 5th edition. W. B. Saunders 



Co., Philadelphia. 

 Janssens, F. A. 1909 La theorie de la chiasmatypie. La Cellule, vol. 25. 

 Lillie, R. S. 1908 Momentary elevation of temperature as a means of pro- 

 ducing artificial parthenogenesis in starfish eggs, etc. Jour. Exp. 



Zool., vol. 5, p. 375. 



1917 Temperature coefficients in the activation of starfish eggs by 



butyric acid. Biol. Bull., vol. 32, no. 3, March. 

 Morgan, T. H., Sturtevant, A. H., Muller, H. J., and Bridges, C. B. 1915 



The Mechanism of Mendelian Heredity. Henry Holt and Company, 



New York. 

 Morgan, T. H., and Bridges, C. B. 1916 Sex-Linked Inheritance in Droso- 

 phila. Carnegie Inst. Wash. Publ. no. 237. 

 Muller, H. J. 1916 Mechanism of crossingover. Amer. Nat., vol. 50. 

 Punnett, R. C. 1913 Reduplication series in sweet peas. Journ. Genetics, 



vol. 3. 

 Snyder, C. D. 1908 Comparative study of temperature coefficients. Amer. 



Journ. Phys., vol. 22, p. 309. 

 Sturtevant, A. H. 1914 Linkage in the silkworm moth. Amer. Nat., vol. 



48, May. 



1917 Genetic factors affecting the strength of linkage in Drosophila. 



Proc. Nat. Acad. Sc, vol. 3, no. 9, p. 555, September. 

 Tanaka, Y. 1913 Gametic coupling and repulsion in silkworms. Journ. Coll. 



of Agric, Sapporo, Japan, vol. 5. 



