Ill] 



THE WEIGHT-LENGTH COEFFICIENT 



99 



Now while this k may be spoken of as a "constant," having 

 a certain mean value specific to each species of organism, and 

 depending on the form of the organism, any change to which it 

 may be subject will be a very delicate index of progressive changes 

 of form ; for we know that our measurements of length are, on 

 the average, very accurate, and weighing is a still more dehcate 

 method of comparison than any linear measurement. 



Thus, in the case of plaice, when we deal with the mean values 

 for a large number of specimens, and when we are careful to deal 

 only with such as are caught in a particular locality and at a par- 

 ticular time, we see that k is by no means constant, but steadily 

 increases to a maximum, and afterwards slowly declines with the 



23 25 27 29 31 33 35 37 39 41 43cms. 

 Fig. 21. Changes in the weight-length ratio of Plaice, with increasing size. 



increasing size of the fish (Fig. 21). To begin with, therefore, the 

 weight is increasing more rapidly than the cube of the length, and 

 it follows that the length itself is increasing less rapidly than some 

 other linear dimension ; while in later fife this condition is reversed. 

 The maximum is reached when the length of the fish is somewhere 

 near to 30 cm., and it is tempting to suppose that with this "point 

 of inflection" there is associated some well-marked epoch in the 

 fish's life. As a matter of fact, the size of 30 cm. is approximately 

 that at which sexual maturity may be said to begin, or is at least 

 near enough to suggest a close connection between the two 

 phenomena. The first step tov^ards further investigation of the 



7—2 



