176 



STRUCTURAL HYBRIDS 



pointed out that they corresponded rather with the lineally arranged 

 genes. Heitz and Bauer (1933) finally put it beyond doubt that the 

 bodies in the nucleus were separate and that each corresponded 

 with a pair of chromosomes. 



The structure of the salivary gland nucleus and its genetical 

 interpretation have now been made clear by the work of Painter, 



/ •vC'' f" """■■■' 







i / 



I ; .' 

 }// 



}{ 





^~ ..._ ^t^, \^..^ J j 



Fig. 59. — Complete nucleus in the salivary gland of ^ Drosophila 

 funebris after pairing is finished (diagrammatic), ch, fused 

 centromeres ; n, nucleolus ; x, inert end of X chromosome ; 

 x', distal end ; y, visible segment of Y ; m, the smallest 

 chromosome pair (Frolowa, 1935). 



Bridges, Roller, Bauer and others (Table 24). Each of the chromo- 

 somes before pairing is marked by transverse bands of characteristic 

 size, number and order. The paired chromosomes in a homozygous 

 larva result from the fusion side by side of pairs of chromosomes 

 which correspond exactly in regard to these bands. Nucleoli are 

 attached to the chromosomes in characteristic positions as in 

 mitosis. In Drosophila all the chromosomes are fused at their 



