Bodies contained in these objects are analogized to cars moving through a traffic jam in a common explanation of a theory resolving their “winding problem.” Lin and Shu’s density wave theory describes these objects, which contain the majority of HII (“H two”) regions. The intrinsic luminosity (-5[1])of these objects is proportional (-5[1])to their asymptotic rotation velocity (-5[1])by the Tully-Fisher (-5[1])relation. Both prongs of Hubble’s “tuning fork” diagram (10[1])contain these (10[1])objects, some (10[1])of which are barred. (10[1])The central bulges of these objects contain supermassive black holes. (10[4]-5[1])For 10 (10[1])points, name these disk-shaped systems of stars, gas, and dark matter, exemplified by Andromeda and the Milky Way. ■END■ (10[1]0[3])