126 CARNEGIE INSTITUTION OF WASHINGTON. 



Duplicate and Plural Determiners, G. H. Shull. 



Dr. Shull's discovery of a clear case of duplicate determiners in the 

 triangular capsules of Bursa has led him to consider generally the whole 

 matter of aberrant heredity of this type. He distinguishes as ''dupli- 

 cate" determiners those which, when separated from each other, pro- 

 duce characters so like that they can not be distinguished from one 

 another, while the term ''plural" determiners (the more inclusive 

 term) comprises two or more genes which independently produce a 

 character or modify it in any way whatever which does not destroy its 

 identity. A useful attempt at an explanation of the origin of duplicate 

 deteiTuiners is then offered, according to which one of a homologous 

 pair of chromosomes containing a determiner (D) becomes displaced in 

 its synapsis, uniting with a chromosome that lacks D. Thus two 

 synaptic pairs come to possess the determiner D, though in a simplex 

 condition; and consequently the determiner, henceforth, behaves as 

 duplicate. A similar result would follow if a determiner alone crossed 

 from one synaptic pair to another. The consequences of the hypothe- 

 sis are followed out in an important paper. 



Cytological Studies on Heredity, C. W. Metz. 



At this Station, from its inception, we have appreciated the import- 

 ance of the study of chromosomes as " bearers " of heredity, and we origi- 

 nally had a laboratory of cytology. A vacancy having arisen (through 

 the resignation of Dr. Gortner) we have secured the assistance of Mr. 

 Charles W. Metz, who began work in June and who reports as follows: 



"Prior to coming here in June I was engaged in a comparative study of the 

 chromosomes in the Diptera, with especial emphasis on the genus Drosophila. 

 This study brought to light a remarkable series of chromosome groups in the 

 Drosophilas, which series was not only very interesting in itself, but showed 

 that the material was exceptionally favorable for study through hybridizing, 

 and through genetic work on individual species. For the latter reason, several 

 species were bred extensively and attempts were made at crossing. The 

 cytological results of these studies were published as ' Chromosome Studies in 

 the Diptera: I. A preliminary survey of five different types of chromosome 

 groups in the genus Drosophila' (Journal of Experimental Zoology, July 1914). 

 Further breeding work was carried on Avith Drosophila ampelophila, in studying 

 the inheritance of the 'apterous character.' The results of this study are 

 in press in the American Naturalist. 



"Since coming here in June I have been carrying on the cytological and gen- 

 etic work which I already had under way, but on a much larger scale, and in 

 addition I have been breeding the beetle Bruchus quadrimacidaius extensively. 

 Of course much of my time has been occupied with securing equipment, getting 

 the laboratory into good working condition, and organizing the investigations. 

 No attempt has been made to complete any investigations, OAving to the short- 

 ness of the time and to the fact that a good deal of the equipment has only 

 recently arrived. The organization of the Laboratory is now almost complete 

 and several lines of study have been considerably advanced, some of which are 



