The Antarctic Convergence is often adopted now as the northern boundary of the ‘Antarctic’ region as a whole, for at least in relation to oceanographic and biological phenomena it is a much more realistic line than the Antarctic circle. It is a well-defined boundary between large water masses, and such a dividing line can be very significant in the distribution of life in the sea, especially of the plankton. About 500 to 700 miles north of it lies the Subtropical Convergence, recognized by a very sharp change of temperature at the surface, and this is clearly the southern limit of many species in the zooplankton and the northern limit of a smaller number in the less varied fauna to the south. It is the boundary between the warm and cold-water epipelagic faunas, and it probably constitutes a real barrier to the dispersal of many species. There is less difference in sea temperatures on the north and south sides of the Antarctic Convergence, but since it is the interface between surface waters of separate origin and distinct properties, and the point at which the layers or currents are changing their depth, we should expect it also to mark certain distribution limits.