- 48 - 



Thus for each individual of loo centimeters there are over 20 individuals 

 that are 25 cm. long, about 10 that are 40 cm., and between three and four that 

 are 60 cm. 



An interesting comparison can be drawn between these figures showing the 

 length-distribution for cod and the corresponding figures for haddock (page 16). 

 Seeing that the cod can become about double as long as the haddock and that 

 its length increases annually on an average about twice as fast, the individuals 

 are spread over a much more extended scale of length. The different divisions 

 of the scale are accordingly passed far more rapidly by the former than by 

 the latter. 



The proportion between the numbers of the different year-classes seems on 

 the whole to be different from what we found was the case with haddock; though 

 it must not be forgotten that the calculations of averages relate only to a period 

 of four years. We have found that different years may have a very varying effect 

 upon the numbers of haddock owing to the great fluctuations in the accession of 

 new individuals. Such fluctuations must seriously affect the mean of a number 

 of measurements relating to quite a short period; since certain years may pre- 

 ponderate unduly. Something similar is the case too with cod. If the cod's 

 yearly variations are not identical with those of the haddock, the averages 

 for the four years will be of little use as a means of comparing the two 

 species, or at any rate a comparison of this nature will be open to suspicion. But 

 even if we feel inclined to doubt the details, it seems at any rate certain that 

 the large individuals (i.e. the older year-groups) of the cod are much 

 more numerous in proportion to the whole aggregate than the 

 corresponding individuals of the haddock, or conversely: that in the 

 North Sea so far as examined young cod are scarcer in proportion to 

 the aggregate of cod than young haddock are among the haddock. 



Of the cod trawled on off-shore grounds sizes under 29 cm. (ii'/a ins) are as 

 a rule classed as unmarketable in Britain (Fulton). The catches of the research 

 steamers contain on an average i-6 individuals of these unmarketable codling, 

 and the whole average-number of marketable is thus not more than 3-2 individuals 

 per trawl-hour. We find then that the number of unmarketable constitutes 

 one third of the whole quantity trawled, while the marketable is ac- 

 cordingly two-thirds: whereas with haddock we found that on an average one 

 seventh of the catch was unmarketable. Thus we see that in comparison with the 

 whole aggregate of the species far more unmarketable cod are taken by trawling 

 than is the case with haddock. The real value of the catches made by the 

 trawlers lies in the amount of haddock taken, and it is therefore worthy of note 

 that while engaged in their work the boats catch quantities of cod that are 

 practically worthless, but which represent a particularly high proportion of the 

 whole aggregate of cod in these localities. 



In England and Scotland the cod brought to market is sorted into two 

 classes, codling and cod^. According to D'Arcy Thompson the boundary line may 



I In what follows we shall employ the word <rorf, in italics, to denote the market-group: thus 

 making a clear distinction between it and the word "cod" denoting the species. 



