THE FUTURE OF WHALES AND WHALING 4O3 



Figure 222. Longitudinal section of a ''wax plug^ from 

 the auditory passage of a Blue Whale, showing ''annual 

 rings'. {Purves, 1955-) 



of the structure of the wax plug, which, as we 

 saw in Chapter 7, is found in the inner part 

 of the external auditory passage of Mysticetes. 

 The plug, which must be freed very carefully 

 from the svurounding tissue, looks like an 

 elongated cone (see Figs. 108 and 222) and 

 consists of layers of cornified epithelium. The 

 plug, particularly in Blue Whales, is often 

 marked by alternate dark and bright bands, 

 which are suggestive of annual rings. Appar- 

 ently the plug grows thicker every year, 

 because the cranial sutures of Mysticetes (just 

 like those of elephants) do not close until late 

 in life, whence the skull and the inner part of 

 the auditory passage keep expanding. To 

 compensate for this expansion, one or two new 

 layers of cornified epithelium are formed 

 across the plug, and Purves believes that the 

 alternate bands around the plug arise from 

 annual periods of maximum growth and 

 maximum rest. Ichihara (1959) points to an 

 alternation of fatty and keratinized degener- 

 ation of the epithelium. Since the bands are 

 by and large made up of the same type of 

 tissue that is found in horns, nails and whale- 

 bone, it seems likely Purves is right in assuming that they, too, arise 

 from annual metabolic changes. Thus, during migrations to and from 

 the Antarctic, the growth will be arrested, and two annual rings 

 Avould be formed, while a single ring only would be formed when, for 

 instance, the southward migration alone influences the metabolism 

 significantly. Other factors, too, might influence the formation of the rings, 

 and Chittleborough and Best (i960) were able to show the presence of 

 rings in the wax plugs of Bryde's Whales, though that species does not have 

 the marked migratory rhythm of Blue, Fin and Humpback Whales, and 

 though it seems to have no restricted breeding season. In the females 

 there was no correlation between ear-plug laminations and corpora 

 albicantia. However, we know very little about these factors, and the only 

 real indication we have that the bands are, in fact, the result of annually 

 recurring events, is that the wax plugs of Blue Whales have more uniformly 



