of the Fishery Board for Scotland. 



149 



the tendency is markedly in the opposite direction later on. In many 

 cases in the very largest fishes a few exceptions also occur, and this may 

 be due to defective nutrition with age, or to the fact that the number of 

 the fishes of large size examined was much less and not sufficient to bring- 

 out the true relationship. It is to be observed that the statement that the 

 law does not accurately apply is supported by that part of the tables and 

 curves where the observations are most numerous, and which, as a rule, 

 includes those fishes which are in adolescence. 



Among cod the greatest number of exceptions were found to occur. 

 The observed weight continued to be greater than that required by the law 

 from 17cm. to 48cm., and then from that point to 69cm., with one or two 

 exceptions, it was less. The number of specimens of the larger sizes was, 

 however, comparatively small, and in the case of the cod many of these large 

 specimens were weighed in May, after they had spawned. In most of the 

 other cases it may be said, although spawning and spent fish are included, 

 the number of these is small ; and the sudden loss of weight immediately 

 after spawning is marked, although it appears to be rapidly regained. 



I am not at present able to offer any satisfactory explanation of the 

 departure from the law of growth generally accepted in the case of fishes ; 

 and perhaps it may be said that the application of this law in biology has 

 not yet been experimentally tested on a sufficient scale among many species 

 of animals. In the growth of some animals there is no doubt that the ratio 

 between the dimensions does not continue constant, and that consequently 

 alteration of shape occurs in the course of growth. In the case of fishes 

 the relation between the length and the weight is in many, and probably 

 most, instances modified in connection with reproduction to a considerable 

 extent, and it may also be altered by the changes which take place in 

 certain of the viscera, as, for example, in the liver, and by the general 

 conditions of nutrition due to season and other circumstances. For 

 obvious reasons, variations in the quantity of food which may be in the 

 stomach or intestine may be neglected. It has to be noted, however, as 

 already stated, that the fishes at periods before reproductive disturbances 

 begin show a marked departure from the law, and that changes arising 

 from difference of season affect fishes at different sizes. 



These tables and curves will also be of value in determining the 

 average weight of specimens of different species belonging to different 

 series or generations, and thus showing the increase of mass from one 

 generation to another as well as the mean weight when the reproductive 

 period is reached and the range of variation. An example may be here 

 given from the plaice to show the amount of growth which may take 

 place from one generation to another, and in the following Table I give 

 the particulars as based on the measurements of over 1800 specimens in 

 a haul in Aberdeen Bay in November : — 



Series. 



Length (Mm.). 



Weight (Grammes). 



Mean 



Kange. 



Average. 



Kange of Mean. 



Average. 



Increase. 





[35—85 



65] 





2-5 





II. 



91—162 



118-1 



6-9—42 



17 



14-5 



III. 



164—260 



216-5 



44—181 



106 



89 



IV. 



261—369 



315 



183—676 



343 



237 



V. 



363—442 



400 



620—970 



708 



365 



VI. 



444—479 



460 



990—1,280 



1,092 



384 



