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The cytological structure of the X chromosome and the DNA organisation of the singed locus were examined in five singed bristle mutants of Drosophila melanogaster. These mutants are all derived from the unstable mutant singed-49, isolated from a wild population in the Russian Far East in 1975. Rearrangements were found at a site within the first intron of the singed gene, where a hobo element is inserted in these mutants. One rearrangement, which is associated with a strong bristle phenotype, has an inversion between 2D and the location of singed at 7D, which separates the singed promoter from the singed coding region. Two phenotypically wild-type derivatives have smaller rearrangements within the first intron which do not appear to interfere with singed expression. Two derivatives with bristle phenotypes have more complex rearrangements, and one of them shows a dominant or antimorphic phenotype. DNA blotting and in situ hybridisation experiments show that, in addition to these rearrangements at a hobo element inserted at singed, other hobo elements in these strains have been mobilised. This system is therefore similar to others in which functional hobo elements continue to transpose, resulting in elevated rates of mutation and chromosome rearrangement.

Workers at the "Apatit" combine, the State Imtitut~ of Mining-Chemical Resources, and MoscowMining Institutehavebeen cooperating in research on thedevelopment of drifting machines forunderground workings In the "Apatit" combine. The workings were drtven through ore. The rocks Include apatite, nepheline, urtite, and other minerals In small amounts. The rocks are maculose, banded-maculose, or banded in structure. The physical properties of the ore depend on its composition, which varies considerably. The hardness of the ore on the Protod'yakonov scale varies from 8 to 16. The tensile strength is 40-90 kg/cm z. Young's modulus is (5-9) 9 l0 s kg/cm z, the linear thermal expansion c06ffictent Is (0.7-2) 9 10 -5 deg-', and the specific heat Is 0.8-1.2 J/g 9 deg.The hardness of the ores and rocks (above eight) prevented the use of cutter-loaders with mechanical rock breaking; therefore, electrothermal breaking was used. First a careful Investigation under operating conditions was carried out; the main laws of electmthermaI breakage and the economic factors were determined, various electromagnetic energy sources were investigated, and the most viable design was chosen and served as a basis for the "business ends" (cutting heads) of the drifting machines.To determine the economic requirements imposed on drifting machines we drove short workings of small cross sectibn with hand rock loading and electrothermal breaking. The data obtained were used in designing experimental models of the drifting machines. We designed two types of cutter-loader for cutting horizontal workings and a machine for driving vertical shafts.The first experimental cutter-loader was based on the PNf3-3K loading machine. In front of the loader we attached a rectangularelectrothermalinstmment: its dimensions and hence those of the driven working, coutd be varied between 5 and 7 m z. The power consumption was 136 kW; it was supplied from the 0.4 kV ac pit power lines. Energy was transmitted to the rock without contact, and the instrument did not exert any mechanical action on the face; as a result it did not weigh more than 120 kg. Breakage began when the instrument-face distance was 0.8-1 m. When this distance was reduced,the energy consumption of breakage decreased, and the rate of advance increased. The rock broken from the face fell onto the floor of the working and was picked up by the loader. For a working cross section of 5 m 2 this cutter-loader gave a rave of advance of 0.3 m/h with an energy consumption ofg0 kWh/m s and a speci~c power at the face of 2.7 W/cm 2. With a working 7 m z in cross section we obtained a rate of advance of 0.28 m/h, an energy consumption of 70 kWh/m s, and a specific power of 1.9 watts per cm 2 of face. The energy consumption was defined as the ratio of the energy taken from the lines to the total rock broken down in the same time. The chief disadvantage of the machine was that the broken rock fell onto the floor of the working, and the loader could not pick it all up, so that the floor was badly cut and the working ...

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