Ill] THE WEIGHT-LENGTH COEFFICIENT 103 



long ; t birth in comparison with other dimensions of the body. 

 It is somewhat curious, however, that this ratio seems to fall off 

 a little in the third year of growth, the animal continuing to grow 

 in height to a marked degree after growth in length has become 

 very slow. The ratio between height and weight is by much the 

 most variable of our three ratios ; the coefficient W jH^ steadily 

 increases, and is more than twice as great at three years old as 

 it was at birth. This illustrates the important, but obvious fact, 

 that the coefficient k is most variable in the case of that 

 dimension which grows most uniformly, that is to say most nearly 

 in proportion to the general bulk of the animal. In short, the 

 successive values of k, as determined (at successive epochs) for 

 one dimension, are a measure of the variability of the others. 



From the whole of the foregoing discussion we see that a certain 

 definite rate of growth is a characteristic or specific phenomenon, 

 deep-seated in the physiology of the organism; and that a very 

 large part of the specific morphology of the organism depends upon 

 the fact that there is not only an average, or aggregate, rate of 

 growth common to the whole, but also a variation of rate in 

 different parts of the organism, tending towards a specific rate 

 characteristic of each different part or organ. The smallest change 

 in the relative magnitudes of these partial or localised velocities 

 of growth will be soon manifested in more and more striking 

 differences of form. This is as much as to say that the time- 

 element, which is implicit in the idea of growth, can never (or 

 very seldom) be wholly neglected in our consideration of form*. 

 It is scarcely necessary to enlarge here upon our statement, for 

 not only is the truth of it self-evident, but it will find illustration 

 again and again throughout this book. Nevertheless, let us go 

 out of our way for a moment to consider it in reference to a 

 particular case, and to enquire whether it helps to remove any of 

 the difficulties which that case appears to present. 



* Herein lies the easy answer to a contention fiequently raised by Bergson, 

 and to which he asciibes great importance, that "a mere variation of size is one 

 thing, and a change of form is another." Thus he considers "a change in the 

 form of leaves" to constitute "a profound morphological difference." Creative 

 Evolution, p. 71. 



