Summary1The accessory respiratory organs of0. punctatusconsist of:–1The supra‐branchial chamber,1the respiratory ‘plates’, and1the respiratory epithelium.2The incomplete division of the supra‐branchial chamber into an anterior and a posterior compartment, the action of the shutter (dendritic plate), the manner of communication between the two compartments and the communication with the pharynx by means of an inhalant aperture are described.3The respiratory plates have a bony medulla, cortex of connective tissue and a richly vascularized epithelium.4The respiratory nodules consists of connective tissue covered externally by a stratified epithelium. Mucous glands and taste‐buds occur on them. Each nodule represents a modified gill lamella and its covering epithelium is derived partly from the wall of the pharynx and partly from the branchial epithelium.5The respiratory epithelium covering the ‘plates’ and ‘nodules’, and lining the supra‐branchial chamber consists of vascular and non‐vascular areas. Each vascular area is studded with ‘rosettes’ of papillae projecting from the epithelium.6The branchial muscles have become modified in several ways in order to suit the changeover from the aquatic to the aerial mode of respiration. InO. striatusthe first, second and the fourth levators are well developed, run over the saccular part of the supra‐branchial chamber and are responsible for its bellowing action. InO. punc‐iatusthe second and third levators have modified into the constrictor supra‐branchi‐alis which fans out on the wall of the posterior part of the supra‐branchial chamber.The non‐vascular part of the epithelium is in the form of irregular ‘lanes’ between the adjacent vascular areas.The presence of pilaster cells and the pattern of the vascular supply to the ‘rosette’ show that the vascular papillae of the respiratory epithelium of the supra‐branchial chamber, the nodules and the plates have been derived from the gill lamellae. Each vascular ‘patch’ or ‘zone’ structurally corresponds to one primary gill lame