The ectoderm thickens in places, with cells changing from cuboidal to columnar. These regions are called '''placodes'''. Placodes may be neurogenic or non - neurogenic. Neurogenic placodes are only found in the head, forming only sensory cells. Morphogenic changes produce the following derivatives: | The ectoderm thickens in places, with cells changing from cuboidal to columnar. These regions are called '''placodes'''. Placodes may be neurogenic or non - neurogenic. Neurogenic placodes are only found in the head, forming only sensory cells. Morphogenic changes produce the following derivatives: |