GENETICS. 13 



It has been found possible to determine the linear order of the genes 

 within any one chromosome pair and to obtain a measure of their 

 distance apart. On the basis of this information, when the position 

 of a new gene has been determined with respect to any two others in 

 its group, it is possible to predict accurately the relations that it will 

 show to any other genes. For the methods used in these analyses, 

 and for numerous other special developments of the subject, the 

 reader is referred to the following publications : 



Brief accounts: 



Wilson, E. B. 1913. Heredity and microscopical research. (Leidy lecture.) Sci- 

 ence, n. s., 37: 814-826. 



. 1914. The bearing of cytological research on heredity. (Croonian lecture.) 



Proc. Roy. Soc. B, 88: 333-352. 



Morgan, T. H. 1915. The constitution of the hereditary material. Proc. Amer. 

 Phil. Soc, 54: 143-153. 



. 1915. Localization of the hereditary material in the germ cells. Proc. Nat. 



Acad. Sci., 1: 420-429. 



and C. B. Bridges. 1916. (Introductory portion of) Sex-linked inheritance 



in Drosophila. Carnegie Inst. Wash. Pub. No. 237, 87 pp., 2 plates. 



Nachtsheim, H. 1919. Die Anatyse der Erbfaktoren bei Drosophila und deren 

 zytologische Grundlage. Zeits. ind. Abst. Vererb., 20: 118-156. 

 Full treatments: 



Morgan, T. H. 1916. A critique of the theory of evolution. Princeton. 197 

 + xpp. 



. 1919. The physical basis of heredity. 305 pp. Philadelphia. 



, A. H. Sturtevant, H. J. Muller, and C. B. Bridges. 1915. The mechan- 

 ism of Mendelian heredity. 262 + xiii pp. New York. 



Babcock, E. B., and R. E. Clausen. 1918. Genetics in relation to agriculture. 

 675 + XX pp. New York. 

 Descriptions of mutants: 



Morgan and Bridges. 1916. (See above.) 



Bridges, C. B., and T. H. Morgan. 1919. The second chromosome group of mutant 

 characters. Carnegie Inst. Wash. Pub. No. 278, pp. 123-304, 7 plates. 



MUTATIONS IN SPECIES OTHER THAN D. MELANOGASTER. 



Several other species of Drosophila have been examined for muta- 

 tions, though none so extensively as D. melanogaster. There is now 

 convincing evidence that mutations occur with something like the 

 same frequency in these species; that the mutants are of the same 

 general nature; that in some cases the same identical mutation has 

 occurred in different species; and that the genetic behavior of these 

 other species is in general very similar to that of D. melanogaster. 

 There follows an abstract of the available data on these species, 

 arranged alphabetically : 



D. ajffinis: Hyde (1915) has reported a "jaunty" wing, inherited as a non- 

 sex-linked recessive. He used the name " confusa" for this species, 

 which was at that time undescribed. 



D. busckii: Warren (1917) found two eye-colors, both recessive and not 

 sex-linked, but apparently lying in the same chromosome. 



D. caribhea: I found a curved wing that was a non-sex-linked recessive 

 (unpublished data). 



