SummaryA description, based on a microscopic study of one species,Leiopelma archeyiTurbott, attempts to provide the first detailed account of development in the New Zealand frog,Leiopelma.Previously only the general features of the intracapsular and post‐hatching development of this frog were known. As far as possible, close comparison has been made with the developmental features of the North American genus,Ascaphus, the only other member of the same primitive Anuran family.The development of the chondrocranium and visceral arches ofLeiopelma archeyiis followed through intracapsular and post‐hatching stages. In the comparative section certain outstanding features of development are considered. An account of previous views on the nature of the basal connection of the quadrate to the neurocranium inLeiopelmaandAscaphusis given. Finally, a theory relative to the basal connection of the quadrate and the nature of the jaw suspension in Amphibia is suggested, and the absence of certain middle‐ear structures in all Urodela and in both these primitive Anurans is disc