Maternal- 



band of 

 (^)256 Chromomcrrs 



Fig 



7. — Diagrams illustrating the structure of salivary gland 

 chromosomes, a = a general view of a salivary gland 

 nucleus with the chromosomes coiled within it. The 

 ' bands ' are shown, but not the threads connecting them. 

 The nuclear sap is shown in black, b — the chromosomes 

 of a salivary gland nucleus in the male Drosophila 

 mclatiogaster spread out by crushing the nucleus. The 

 maternal parts of the paired chromosomes are shown in 

 black, the paternal parts white. Chr. = chromocentre 

 (stippled) ; Nuc. = the nucleolus. II L and II R are 

 the two arms of the Ilnd chromosome, III L and III R the 

 two arms of the Illrd chromosome ; the IVth chromo- 

 some and the X and Y chromosomes (the latter very small) 

 are also shown. An inversion (Inv.) is shown in the 

 ' right ' arm of the Ilird chromosome, c = a diagram of 

 a small part of a salivary gland chromosome, composed 

 of 2r)6 threads, 128 paternal and 128 maternal, d = adia- 

 gram illustrating how the chromocentre is made up (in 

 the female of D. melanogaster) by a fusion of the inert 

 parts of all the chromosomes (represented by stippled 

 bands). 



