  While directed site-animals have been solved on several lattices, directed
bond-animals remain unsolved on any non-trivial lattice. In this paper we
demonstrate that the anisotropic generating function of directed bond-animals
on the square lattice is fundamentally different from that of directed
site-animals in that it is not differentiably finite. We also extend this
result to directed bond-animals on hypercubic lattices.
  This indicates that directed bond-animals are unlikely to be solved by
similar methods to those used in the solution of directed site-animals. It also
implies that a solution cannot by conjectured using computer packages such as
GFUN or differential approximants.
