On the development of the auditory apparatus in Sphenodon punctatus

This memoir contains a detailed and fully illustrated account of the development of the auditory apparatus and associated structures in the New Zealand Tuatara. As this important type is on the verge of extinction, it was thought desirable to treat the subject fully, although, as might have been expected, the developmental history agrees closely with that found in other reptiles. The work was carried out chiefly by means of wax plate reconstruction models. The development of the pharynx and its derivatives, the thyroid and thymus glands and the trachea, was investigated and appears to follow the normal course. The first visceral cleft undergoes some closure from below upwards and the process is completed by the apposition of the anterior and posterior borders of the cleft. The second and third visceral clefts are closed by a backwardly-growing operculum, while the fourth visceral pouch is imperforate and bears a rudimentary fifth visceral pouch as an evagination of its posterior surface.