THE WAX PLUG IN THE EXTERNAL AUDITORY 

 MEATUS OF THE MYSTICETI 



By P. E. Purves 



Department of Zoology, British Museum 

 (Natural History) 



{Received 9 March 1955) 



(Plates XIV-XVIII; Text-figs. 1, 2) 



INTRODUCTION 



he external auditory meatus of the Cetacea, because of its extreme smallness, seems to have 



T. 



attracted the attention of anatomists since the earliest times, and various descriptions exist of its 

 external form, anatomy and histology. Buchanan (1828), who appears to have been a specialist in the 

 subject of the ceruminous secretions of the ear, discovered in the meatus of Balaena mysticetus an 

 'unctuous cerumen of a greyish blue colour', and Carte and Macalister (1869) stated that the meatus 

 of Balaenoptera acutorostrata was 'filled with a dark, greyish sebaceous substance, produced in 

 ceruminous glands, the openings of which were visible on the mucous membrane '. These descriptions 

 seem to indicate that the anatomists just mentioned were concerned only with the soft, pigmented 

 secretion which is to be found abundantly in the distal parts of the meatus of all the larger Cetacea. 

 Lillie (1910) made a detailed study of the whole length of the auditory meatus of several of the larger 

 Cetacea during his researches at the Whaling Station at Inniskea in the west of Ireland, and found 

 that in the ' meatus of all individuals examined there was a solid plug of wax-like substance of fairly 

 definite size and shape, which did not seem to have been hitherto described'. Turner (19 13) gave an 

 account of a number of wax plugs from Megaptera longimana and Balaenoptera physalus which came 

 into his possession, and the descriptions and figures agree very closely with Lillie's original account 

 of the wax plug of the latter species. That Turner wrongly imagined the plug to be secreted by the 

 distal end of the meatus was pointed out by Lillie (191 5). 



In the course of their investigations on the sense of hearing in the Cetaceans, Fraser and Purves 

 (1954) found it necessary to test the sound conductivity of the external meatus and adjacent structures 

 in the Mysticeti, and were able, through the generosity of the Hector Whaling Company, and the 

 co-operation of the National Institute of Oceanography, to obtain during 1953 and 1954 two large 

 frozen portions of the squamo-mastoid region of Balaenoptera physalus. The external meatus was laid 

 open along its entire length, and although the wax plugs of both specimens were badly damaged, 

 sufficient material remained to indicate that Lillie's and Turner's description requires some modifica- 

 tion. The sound attenuation of this apparently highly damping substance was found to be less than 

 1 db. throughout its length, and this surprising result led to a closer examination of the structure as a 

 whole. Microscopic sections were cut from fragments taken from the two specimens of Balaenoptera 

 physalus, and two of Lillie's three specimens from this species were radiographed, the remaining 

 specimen being bisected longitudinally at its widest diameter. 



