In any case, an axis has been determined and a pattern set up. We have a slight problem here. We could say that gravity, the signal, follows the ideas of Baldwin and Lamark and becomes incorporated into the genome. This is difficult, and we shall come back to it later. It does seem that in some animals the gravitational signal has been mimicked by an internal signal.
Most animals are somewhere in between.
The organism we have made, the blastaea, is radially symmetrical. In sexually reproducing animals like frogs this is often defined by the point of entry of the sperm. This separation of the specification of differences from the origin of a cell by means of a signal gives us the concept of positional information. Almost all animals have genetic information which specifies position along an axis e.g. homeobox genes which we shall consider in due course. Francis Crick remarked that embryos seem to be very fond of stripes.