Lines oblique to the growing edge result from traveling waves of pigment production (right figure). In the model, they result if the activator has a small diffusion range while the antagonistic substance is nearly non-diffusive. An activated region can "infect" its neighboring region such that, after a certain lag phase, it becomes fully activated too, and so on. The situation is very similar to the wave-like spread of an epidemic. One person can infect its neighbors. The full development of a sickness is also based on a self-enhancing effect, the replication of the virus. Some time after bursting virus proliferation, the immune system begins to acts antagonistically. It captures the virus and the person will become healthy again. For the spread of the epidemic it is crucial that only the virus, but not the immune response is transmitted from one individual to the next. In the time record on the shells, this leads to oblique lines. V-like tips are the record of an annihilation of two waves.
A common aspect in many of these patterns is the involvement of a second antagonistic reaction that extinguishes concentration maxima shortly after they have been build up, causing the permanent modification of the spatial pattern. The following shell is an example: