238 THE VARIATION, RACES AND MIGRATIONS OF THE MACKEREL. 



plan of investigation was decided upon, and that a number of fisli 

 caught at Plymouth during the summer of 1897 were so much smaller 

 than any from other localities (from 4 to 9 inches in length), that I 

 have thought it better to reserve most of the results of their examination 

 until a sufticient number of young forms has been also obtained from 

 other parts. These small fish are frequently taken in sprat seines, weirs, 

 and in other ways on various parts of the British coast, and I should be 

 much obliged to any who read these lines, and have the opportunity of 

 assisting, if they would kindly forward to me any specimens of the 

 common mackerel they may come across below 8 inches in length. 

 They should be forwarded fresh (but damp) by post, if in small quantity; 

 or in seaweed or ice by train, if in quantity ; and the locality, date, and 

 method of capture should be recorded. The cost of carriage, &c., will 

 be willingly paid by the Association. 



As regards the condition of the fish in the different consignments 

 under examination, I should say that the Plymouth fish have been 

 examined in a perfectly fresh condition, but that all other fish, except 

 those in two Irish consignments, have been iced before examination, in 

 order to enable them to withstand the effects of a more or less lengthy 

 journey by rail or sea. The two Irish consignments referred to were 

 those dated Kinsale, July 30th and September 3rd, 1897. These fish 

 arrived during my absence in Canada, and after measurement were placed 

 in tanks of formaline to await my return. With this exception, the 

 condition of the different consignments at the time of examination may 

 be regarded as practically uniform, so far as external characters are 

 concerned. The viscera of the fish from Brest, and of some of the 

 earlier Irish samples were, however, so rotten, owing to delays in transit, 

 that no attempt was made to record the sexual condition of all the fish 

 in these particular samples. 



After this introduction I may proceed at once to describe the methods 

 and results of the investigation up to the present time. 



I. The Method of Investigation. 



As all attempts to discover constant individual peculiarities in the 

 mackerel of any one locality, as compared with those from any other, 

 have completely failed, it is clear that, in order to determine whether 

 local races exist or not, recourse must be had to the detailed study 

 of the variation of certain chosen characters in the fish of different 

 localities. The range of variation in these different local groups of 

 fish can then be compared, and the frequency with which particular 

 variations, or combinations of variations, occur in any one group can be 

 compared with its frequency in all the others. Thus, if we suppose 



