ADAPTATION 177 



kind, when for instance, as shown by Babak, 1 the intestine 

 of tadpoles changes enormously in length and thickless 

 according as they receive animal or vegetable food, being 

 nearly twice as long in the second case. Besides this the 

 so-called mechanical adaptations are of the greatest interest. 



It has long been known, especially from the discoveries 

 of Schwendener, Julius Wolff, and Eoux, that all tissues 

 whose function it is to resist mechanical pressure or 

 mechanical tension possess a minute histological structure 

 specially suitable to their requirements. This is most 

 markedly exhibited in the stem of plants, in the tail of the 

 dolphin, in the arrangements of the lime lamellae in all 

 bones of vertebrates. All these structures, indeed, are such 

 as an engineer would have made them who knew the sort 

 of mechanical conditions they would be called upon to 

 encounter. Of course all these sorts of mechanically 

 adapted structures are far from being "mechanically ex- 

 plained," as the verbal expression might perhaps be taken 

 to indicate, and as indeed has sometimes been the opinion 

 of uncritical authors. The structures exist for mechanics, 

 not ly it. And, on the other hand, all these structures, 

 which we have called mechanically " adapted ' ones, are far 

 from being mechanical " adaptations," in our meaning of the 

 word, simply because they are " adapted." Many of them 

 indeed exist previous to any functioning, they are for the 

 most part truly inherited, if for once we may make use of 

 that ambiguous word. 



But, the merely descriptive facts of mechanical adapted- 



1 Arch. Entw. Mech. 21, 1906. By a very detailed comparative study 

 Babak was able to prove that it is the plant proteids to which the effect of 

 vegetable food is chiefly due ; thus we have an adaptation to digestibility. 

 Mechanical circumstances are only of secondary importance. (See also Yung.) 



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