The hair tracts of Marmosa cinerea, M. murina, Chironectes minimus. Didelphis marsupialis var. azarae, Didelphis marsupialis var., Didelphis sp. and Metachirus oppossum, all members of the marsupial family Didelphidae are recorded.
The several tract patterns are shown to be classifiable into a series of stages of increasing complexity in terms of divergent and convergent centres.