264 



WHALES 



Strength. A hollow cylinder has practically the same degree of rigidity as 

 a solid one, just as a T-beam has the same strength as a solid beam. More- 

 over, in the baleen, the tubes allow for inner movement, just like the leaf 

 spring of a motor-car, and are therefore more elastic than a solid tube 

 would be. The tubes run uniformly along the entire length of the baleen 

 and emerge as hair on the inner edge (see Fig. 143). On closer investiga- 

 tion the hair does, in fact, prove to be hollow, and open at the tip where 

 it is constantly worn down by friction. For, needless to say, the plates are 

 exposed over their entire surface, to continuous friction by contact with the 

 water, and on the inside also by movements of the tongue. Similarly, our 

 own epidermis is constantly worn off by rubbing. Like it, and like our 

 hair, the baleen must continuously be replenished at its root, in this case 

 the gum. As the top wears off, new material is continuously being pushed 

 out of the gum, so that the baleen retains an even length, or grows to its 

 proper length in young animals. In order to obtain a better idea of this 

 process, we shall look at the development of the plate in the foetus. At birth 

 a whale has very small and soft baleen plates, and while it is being suckled, 

 it has, in fact, no need of them. Very young foetuses still have completely 



Figure 142. Whenever a solid beam (e.g. a 

 rubber rod) is bent, its convex side becomes 

 longer and its concave side shorter. Thus the 

 rod must withstand tension and compression. 

 In the centre, the length remains constant 

 and no external forces act upon it. A hollow 

 pipe is therefore as strong as a solid one. 



Figure 143. Highly diagrammatic sketch of a 

 section through the head of a Rorqual, show- 

 ing position and structure of baleen. U = 

 upper jaw ; G = part of baleen eriibedded in 

 the gum, where new baleen is formed and 

 pushed out; Hp -- horny tubes which 

 emerge on the inner side as hair (Ha). 

 Friction takes place over the entire surface 

 of the baleen protruding from the gum (S). 



