xi THE ELEMENTS OF STRUCTURE 215 



ably suited to the function. Every animal is a bundle 

 of adaptations, which have been wrought out through 

 ages and have often attained a high degree of perfection. 

 Disharmonies are sometimes to be detected, especially 

 when the organism is changing its habitat or habits, but 

 they are few and far between. When we consider organs 

 such as the eye, the heart, the kidneys, the placenta 

 binding mother and young together in their intimate 

 ante-natal symbiosis, we discover a multitude of subtle 

 adaptations ; and " the narrowest hinge in my hand 

 puts to scorn all machinery ' for the perfection of 

 mammalian joints is extraordinary. When the modern 

 zoologist speaks of the adaptation of an organ he means 

 not only that it is fit, effective, and well-adjusted, but 

 that it is a product of a long process of evolution the 

 theoretical interpretation of which is still a very difficult 

 problem. Some well-shaped structures, like the heart, 

 are for the most part concerned with the internal economy 

 of the body ; others, like limbs, are mainly significant 

 in relation to the environment. But there is no hard 

 and-fast line here, for the ptarmigan's heart is specially 

 adapted to high altitudes and the antelope's to the neces- 

 sity of rapid escape on the plains. Some adaptations are 

 mainly structural, as we see in the strong arch of a 

 tortoise's carapace, and others mainly functional, as in 

 the arrangements for regulating the temperature of the 

 blood in birds and mammals ; but the two aspects are 

 inseparable. Some of the most exquisite adaptations are 

 those that secure the harmonious co-operation of different 

 parts of the body, as when the mother-mammal is pre- 

 pared for her offspring before its development begins, 

 during the ante-natal life, and after it is born. 



From amid innumerable adaptations l we select one 

 other instance, that of an African egg-eating snake, 

 Dasypeltis scabra, a weak-bodied creature less than a 

 yard in length, which is able to swallow birds' eggs three 

 times the diameter of the thickest part of the body. The 

 jaws are almost toothless, but a few posterior teeth are 

 present which serve to grip the egg. There is the usual 



1 See the^author's Wonder of Life, p. 523 (Melrose : London, 1914). 



