THE LAMARCKIAN PRINCIPLE 55 



move with little jerks. But we cannot connect that with the 

 growth of their flinty coating or of the sheltered cell within. 

 If an organism is to grow, it needs food, power of assimilation, 

 and means of distributing nourishment to its different parts. If 

 it is an animal, it must in addition have oxygen to breathe. But 

 for growth pure and simple, exercise is not wanted by an animal 

 any more than it is by a vegetable. A chicken within the egg 

 has little opportunity for taking exercise : yet, cramped in his 

 narrow prison, he goes through the most important stages of 

 development and at length emerges, able to move about, en- 

 dowed with something in the way of instinct and with brain 

 sufficient to learn quickly from his mother's teaching. The 

 altrices, the birds which are born helpless and remain for a time 

 in the nest, attain almost their full size before they take any 

 vigorous exercise. A young albatross is fed up till he is a 

 perfect mass of fat and heavier than either of his parents ; in 

 this condition they leave him in the nest to develop. And as 

 everyone knows, he does staying sedentary in the nest grow 

 into a very glorious bird. 



The embryo of any of the higher mammals passes through a 

 wonderful series of changes, and is structurally not far from the 

 mature phase, when at length it sees the light and knows the 

 delights of exercise and play. In a later chapter (pp. 117, I2l) 

 I shall return to the subject and try to explain the role that is 

 assigned to exercise in nature. Enough has been said to show 

 that it is not at the disposal of Lamarckism. 



If exercise is not necessary to growth, it would seem to follow Disuse 

 that disuse, even if almost complete, will not arrest development 

 altogether. In some cases it certainly does not. Even when 

 for good and intelligible reasons growth has become associated 

 with constant exercise, we do not find a very great shortcoming 

 in a particular organ of which little use is made. In some 

 breeds of domestic ducks that have given up the habit of flight, 

 the wing bones (humerus, radius, carpo-metacarpus) are in 

 actual measurement longer than in the wild duck (Anas boscas\ 

 though shorter relatively to the leg bones. No doubt the wing 

 development is less than it would be with more active habits. 



