BIOLOGY. 



375 



Morgan, T. H., A. H. Sturtevant, and C. B. Bridges, Columbia University, 

 New York. Study of the constitution of the germ-plasm in relation to 

 heredity. (For previous reports see Year Books Nos. 15-19.) 



At the present time we are carrying about 240 different stocks of 

 Drosophilas. The number of stocks is continually increasing (owing 

 to the discovery of new mutations), although we frequently discard old 

 ones in favor of more useful combinations. The stocks are being 

 improved by the addition of mutants and combinations of mutants 

 that have a special value for new lines of work. For example, new 

 dominants, if viable, are nearly always retained on account of their 

 value in preparing stocks for experiments; mutants that fill in gaps in 

 the ' 'chromosome maps" are kept for finding out what is happening 

 in that particular part of the ''chromosome"; new linkage combina- 

 tions of already known mutants are made up, for they enable us to 

 detect any changes whatsoever that may take place in a particular 

 "chromosome." 



Map of Drosophila melanogasier. N^ov. 7, 1921. 



