Neurogenic placodes: a common front.

Neurogenic placodes are specialized regions of the embryonic ectoderm that are central to the development of the cranial sensory systems of vertebrates. These structures generate many of the sensory neurones of the head and also, in some instances, the associated sensory receptor cells. The neurogenic placodes have often been thought to share common pathways of development and to have evolved together. However, recent work has shown that this is not the case. The term 'neurogenic placodes' no longer seems to describe a cohesive group. Rather, the neurogenic placodes fall into a number of categories, and it is within each of these that the members share a common development and evolution.