100 



THE RATE OF GROWTH 



[CH. 



apparent coincidence would be to determine the coefficient k of 

 the two sexes separately, and to discover whether or not the point 

 of inflection is reached (or sexual maturity is reached) at a smaller 

 size in the male than in the female plaice ; but the material for 

 this investigation is at present scanty. 



A still more curious and more unexpected result appears when 

 we compare the values of k for the same fish at different seasons of 

 the year*. When for simphcity's sake (as in the accompanying 

 table and Fig. 22) we restrict ourselves to fish of one particular 



Fig. 



JFMAMJ JASONDJ 

 22. Periodic annual change in the weight-length ratio of Plaice. 



size, it is not necessary to determine the value of k, because a 

 change in the ratio of length to weight is obvious enough ; but 

 when we have small numbers, and various sizes, to deal with, 

 the determination of k may help us very much. It will be seen, 

 then, that in the case of plaice the ratio of weight to length 

 exhibits a regular periodic variation with the course of the seasons. 



* Cf. Lammel, Ueber periodische Variationen in Organismen, Biol. Centralhl. 

 xxn, pp. 368-376, 1903. 



