ELECTRON MICROGRAPH MAP OF THE DROSOPHILA-MELANOGASTER POLYTENE CHROMOSOME-3R DIVISION-81 THROUGH DIVISION-90

The banding pattern of the proximal half of the polytene salivary glan d 3R chromosome of Drosophila melanogaster was studied with thin secti on electron microscopy. Bands were identified according to Bridges' re vised light microscopic map, which contains 330 single and 121 double bands within the regions 81 through 90. We found a total of 447 bands in this region. 97 Bridges' single bands were easily detected in almos t all thin sections, while 177 faint bands could be seen only in some micrographs. 56 Bridges' single bands could not be found. 32 Bridges' doublets were made up of two separate bands each in thin sections. The other 89 Bridges' doublets seemed to be either single bands or remain ed obscure. A total of 20 small new bands, which were not drawn on Bri dges' map, were detected.