112 CARNEGIE INSTITUTION OF WASHINGTON. 



of the National Research Council he cooperated in the report of the 

 committee concerning physical criteria for the selection of recruits. 

 Dr. J. A. Harris, besides carrying on here his extensive series of breed- 

 ing experiments on beans, went to Florida and to the Dismal Swamp, 

 North Carolina, to study the relations of tissue sap to the environment 

 of plants. Dr. A. M. Banta, assisted by Mr. Obreshkove, has con- 

 tinued his extensive breeding experiments on sex in daphnids and has 

 been getting into final form for publication his work on selection of 

 strains of daphnids for sensitiveness to hght. Dr. O. Riddle completed 

 his editorial work on the Whitman manuscripts and is preparing a book 

 embodying his researches on sex in pigeons. Dr. E. C. MacDowell, 

 assisted by Miss Vicari, has continued his work on the effect of alcohol 

 on the germinal qualities of rats. Dr. C. W. Metz continued his 

 study on the evolution of the germ-plasm of Drosophilidse. Dr. A. F. 

 Blakeslee continued his genetic studies on plants and directed the work 

 on poisons of the bread-mold carried on at this Station at the expense 

 of the U. S. Department of Agriculture. He is also improving the 

 adzuki bean as "an emergency war-research problem." During July 

 to September Dr. Aute Richards, of Wabash College, was a guest at 

 the Station, studying, cytologically. Dr. Banta's sex-intergrading 

 daphnids; also. Dr. John Y. Pennypacker, of the University of Pennsyl- 

 vania, studied, histologically, abnormal seedling beans. 



REPORTS ON INVESTIGATIONS. 



THE GERM-PLASM AND ITS MODIFICATION. 

 COMPARATIVE STUDY OF THE CHROMOSOME GROUPS IN DIPTERA. 



Dr. Metz has during the year devoted some time to extending his 

 studies on the chromosomes in the Diptera, and especially on their 

 behavior in spermatogenesis. He has almost completed a study on 

 spermatogenesis in the AsiUdse and one on spermatogenesis in the 

 DrosophiUdse. Since the chromosomes are doubtless to be regarded 

 as the true specific stuff, a study of their forms, and especially of the 

 evolution of the chromosomal complex, becomes of great interest. 

 Dr. Metz has shown that, starting with the generalized form found in 

 Drosophila ampelophila, 12 types of chromosome-complexes may be 

 distinguished in related species which are merely modifications of that 

 generaUzed form. These types are shown in figure 1 . It will be seen 

 that A consists of 3 pairs of large chromosomes and 1 pair of small 

 ones. Of the 3 large pairs one (the lower in each drawing) is the sex- 

 chromosome pair. Of the others one or both may be divided, resulting 

 in 4 or 5 large pairs. Thus in F there are 5 pairs of large chromosomes 

 and 1 pair of small ones. The foregoing series doubtless represents 

 stages in the evolution of the chromosome-complex — the germ-plasm — 

 of one group of genetically related organisms. 



