THE DEGENERATION OF ARMOUR IN 



ANIMALS 



By FELIX OSWALD, D.Sc, B.A., F.G.S. 



In tracing out the history of many classes of animals it is 

 impossible for the palaeontologist not to be impressed with the 

 fatal effect which an ever-increasing development of armour 

 inevitably produces upon the vitality and persistence of a race. 

 A long continuance of special and uniform conditions of environ- 

 ment would appear to favour a stead}- progression in the 

 development and elaboration of the exoskeleton for defensive 

 purposes. This tendency may be carried on to so great an 

 extent as to sacrifice plasticity of structure, as well as all 

 variation in the direction of plasticity, to the attainment of a 

 more complete protection with the aid of armour. Whenever 

 new and adverse conditions of existence arise, those races which 

 have adopted such means of defence find themselves severely 

 handicapped in their struggles to cope with their altered sur- 

 roundings ; they are unable to vary adequately and, as an 

 inevitable natural consequence, eventually die out. It would 

 indeed appear that only species which can revert, more or less, 

 to the original flexibility of their ancestral forms or which 

 have to some extent retained their flexibility, can give rise to 

 suitable variations, capable of developing on fresh and successful 

 lines of evolution. In short, this tendency may be briefly 

 enunciated in the form that, in response to change of en- 

 vironment, reduction of armour is essential to the preservation 

 of the race. Even in the history of human warfare the new 

 conditions which arose from the invention of gunpowder 

 exercised an analogous effect upon the reduction of armour, 

 the burden of which had increased to so great an extent that 

 when a mediaeval knight was knocked off his horse in the 

 shock of battle he often lay helpless and disabled by the very 

 weight and complexity of his armour. 



Among Vertebrates perhaps the most striking instance of the 



abandonment of armour in an ancient class is afforded by the 



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