THE FUTURE OF WHALES AND WHALING 



401 



Figure 221. Variations in thickness in the baleen plates of a Fin Whale, showing Prof. Ruiid's 

 annual levels. {Ruud, 194-5.) 



thicker at the bottom, since the top has been exposed to longer friction 

 than the rest.) 



Oddly enough, the plates are not thickened uniformly. Thus the 

 lines shown in Figs. 220 and 221, are made up of so many crests and 

 n-oughs which can be seen with the naked eye. If we assume - and there 

 is no reason to do other\vise - that frictional effects are equal over the 

 entire surface of the baleen plate, the ridges must be due to the fact that 

 different quantities of horn are deposited in the cortical layer from time to 

 time. On p. 267 and in Fig. 145, we have seen that the thickness of the 

 cortical layer is determined in a very narrow area of the gum. Every 

 difference in thickness corresponds with differences in horn production 

 during a very limited time. Why new horn should not be laid down con- 

 tinuously is not quite clear, but is most probably due to periodic metabolic 

 changes. Unfortunately we know little about similar processes in other 

 animals, except that, in human beings, malnutrition causes the growth of 

 hair and nails to be impaired or even to be discontinued. Ex-prisoners of 

 concentration camps and particularly of the notorious Japanese hunger 

 camps will be able to bear this out from personal experience. Moreover, 

 friction itself can also stimulate the formation of horn, for as Le Gros 



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