Analysis of Cytoplasmic Structures. 57 



that is, giving approximately 50 per cent, crossing over between 

 each lethal and "short." This shows more crossing-over than is 

 known to occur in the X-chromosome of other species of Drosophila 

 and may correspond to the greater length of the X-chromosome 

 in obscura. 



Further breeding tests showed the presence of two separate 

 sex-linked lethals and agreed with the original assumption as to 

 their loci. One (1 2 ) was found to be very close to the locus for 

 "beaded " and gave 10 cross-overs with it in 155 males. " Beaded" 

 was already known to be far enough from short to show no appre- 

 ciable linkage to it. The other lethal (1 3 ) was independent of 

 "beaded" but showed some linkage to "short" by a ratio of 21 

 "short" to 34 "not-short" males, while the number of "beaded" 

 and "not-beaded" males was equal. That established its locus 

 in the other end of the chromosome from (1 2 ) with "short" 

 between. 



33 (1493) 



New methods for the analysis of cytoplasmic structures. With 



demonstrations. 



By Robert H. Bo wen (by invitation). 



[From the Department of Zoology, Columbia University.] 



The year 1898 marked the recognition of two fundamental 

 cytoplasmic structures, — mitochondria and the Golgi apparatus. 

 The mitochondria soon became of interest to every biologist 

 through Meves' theories concerning their importance in cellular 

 differentiation and inheritance, but we are still very much in 

 the dark regarding many features of their behavior. The Golgi 

 apparatus, on the other hand, was almost forgotten and until 

 recently even its status as an independent cytoplasmic element 

 was in doubt. The last few years have witnessed in Europe a 

 revival of interest in these and other cytoplasmic inclusions, an 

 interest not yet fully reflected in this country. It would seem, 

 then, an opportune time for calling the attention of biologists 

 to these structures, so little reckoned within our physiological 

 concept of the cell. 



