178 STRUCTURAL HYBRIDS 



these granules makes a band, and they are connected by deHcate 

 threads to successive granules along the chromosome. In other 

 words each of the i-)airing chromosomes has divided four or five 

 times, and the products of its division have remained in side-by-side 

 association (Bridges, 1935 ; Metz, 1935 ; KoUer, 1935). It is 

 possible that they are associated closely in pairs resulting from 

 primary attraction and that these pairs are more loosely held 

 together by a secondary attraction corresponding to the secondary 



Table 24 

 Observations of Salivary Glands in Diptera 



Drosophila nielanogaster . 



KostofJ, 1930. 



Painter, 1934, a and b. 



Bridges, 1935, 1936. 



Koltzoff, 1934. 



MuUer and Prokofieva, 1935. 



Ellenhorn, Prokofieva and Muller, 1935 {in vivo). 



Roller, 1935. 

 D. simulans, and D. melanogaster x D. simiilavs. 



Patau, 1935 {in vivo). 

 D. pseudo-obscura. 



Koller, 1935, 1936. 



Tan, 1935. 

 Chironomus spp. 



Balbiani, 1881. 



Bauer, 1935, a and b {in vivo). 



King and Beams, 1935. 



Koller, 1935. 

 Bibio hortulanus. 



Heitz and Bauer, 1933. 

 Simulium. 



Bauer, 1935. 

 Sciara spp. 



Metz, 1935. 



attraction characteristic of somatic chromosomes in the Diptera 

 (Ellenhorn, Prokofieva and Muller, 1935). The original plane of 

 association of the paired multiple chromosomes is, however, soon 

 lost, and the whole bundle of threads becomes a uniform cylinder, 

 a polytene chromosome, as we might call it. 



The knowledge that exactly corresponding parts of chromosomes 

 pair in salivary gland nuclei has facilitated a closer analysis of the 

 genetic structure of Drosophila in two ways. First it has been 



