320 ADAPTIVENESS AND PURPOSIVENESS 



narrowest hinge in my hand puts to scorn all machinery''; 

 the hand as a whole is the subject of a Bridgewater Treatise. 

 The Vertebrate eye is extraordinarily well adapted, in spite 

 of the instrumental imperfections which Helmholtz discov- 

 ered. The functional correlations of internal organs such 

 as heart and lungs are as effective as they are delicate. The 

 flat-fish is so adaptable in its coloration to the pattern of 

 the sea-floor on which it rests that it has practically a Gyges 

 ring, making itself invisible, sometimes almost instantane- 

 ously. Flowers and their welcome insect-visitors are suited 

 to one another as glove 'to hand. The realm of organisms 

 abounds in adaptations, some extraordinarily perfect, some 

 in process of becoming perfect. 



First there are the structural adaptations of the organism 

 — some with internal and some with external reference, 

 some static, some dynamic. The internal structure of a long 

 bone or of the stem of a plant is suited in detail to stand 

 the strains and stresses to which it is exposed. The same 

 quality of architectural stability may be seen everywhere 

 from the scaffolding of a siliceous sponge like Venus's Flower 

 Basket to the spine of a sea-urchin, from the spirally twisted 

 encasement of an arenaceous Foraminifer to the prismatic 

 structure of the enamel of our teeth. 



Less static are the adaptations of parts that move and 

 work. The adaptations of a bird's skeleton for flight and 

 for bipedal progression are many and thorough. The heart 

 is a masterpiece of fitness, and in many cases, as in the 

 antelope on the plains or in the ptarmigan on the high moun- 

 tains, there are interesting special adaptations of the heart 

 to stand special strain. The delicacy and complexity of the 

 mouth-parts of such insects as mosquitoes may well evoke the 

 artificer's admiration. 



