Development of the olfactory and vomeronasal organs in Discoglossus pictus (Discoglossidae, Anura).

Using histological techniques and computer-aided three-dimensional reconstructions of histological serial sections, we studied the development of the olfactory and vomeronasal organs in the discoglossid frog Discoglossus pictus. The olfactory epithelium in larval D. pictus represents one continuous unit of tissue not divided into two separate portions. However, a small pouch of olfactory epithelium (the "ventromedial diverticulum") is embedded into the roof of the buccal cavity, anteromedial to the internal naris. The lateral appendix is present in D. pictus through the entire larval period and disappears during the onset of metamorphosis. The disappearance of the lateral appendix at this time suggests that it is a typical larval organ related to aquatic life. The vomeronasal organ develops during hindlimb development, which is comparatively late for anurans. The development of the vomeronasal organ in D. pictus follows the same general developmental pattern recognized for neobatrachians. As with most anurans, the vomeronasal glands appear later than the vomeronasal organ. After metamorphosis, the olfactory organ of adult D. pictus is composed of a series of three interconnected chambers: the cavum principale, cavum medium, and cavum inferius. We suggest that the ventromedial diverticulum at the anterior border of the internal naris of larval D. pictus might be homologous with the ventral olfactory epithelium of bufonids and with the similar diverticulum of Alytes.