242 THE VARIATION, RACES AND MIGRATIONS OF THE MACKEREL. 



These three characters, in fact, depend upon a formation of pigment 

 in the superficial layers of the skin, apparently different in kind from 

 that which brings about the transverse bars and intermediate spots. 

 Some further study of the pigmentation of the mackerel will be 

 necessary before their value for racial determinations can be assured. 

 This objection does not apply, it is true, to the last character enumer- 

 ated (No. 11) ; but my records of the variation of this character were 

 commenced much later than those of all the others, and are not yet 

 sufficient to yield any general results. 



The investigation in hand accordingly rests upon an examination of 

 the variation of seven characters, of which six are numerical and one 

 morphographical. Four of these characters deal with the characteristic 

 markings of the fish, and three with the structure of the dorsal fins. 



It will be noticed that the number of transverse bars has been 

 recorded twice for each fish; firstly, as an entire series, and secondly, 

 between certain arbitrary limits. This has been done with a view 

 to expose any errors which might arise from the fact that the bars 

 are not always distinct and parallel, but are frequently branched and 

 anastomosed with one another, broken, or otherwise irregular, rendering 

 the task of enumeration not aUvays easy, and so introducing a certain 

 subjective element into the records. Now the number of bars, or 

 portions of bars, which cross or meet the lateral line admits of fairly 

 exact enumeration, and seemed to me to offer an excellent method 

 of checking the estimate formed of the number of bars in the entire 

 series. In this expectation I have not been disappointed, as the 

 discussion of tables B and C will reveal, although the fact that the 

 course of the lateral line itself is also subject to slight variations has 

 naturally prevented an absolute correspondence in all details between 

 the two modes of enumeration. 



It only remains to add that the number of transverse bars and of 

 intermediate spots, together with the data concerning the shape of 

 the bars, have all been determined upon the same side of the fish, 

 viz., the left. I frequently took note of the condition of the right side 

 of the fish also, but these notes are nowhere referred to in the present 

 report, and are not incorporated in any of the tables. 



III. Particulars Concerning the Consignments of Mackerel 



Investigated. 



In this section are given the place, date, and method of capture, the 

 name of the consignor, and such other information as may bear upon 

 the authenticity and representative character of the samples. All the 

 samples were forwarded to Plymouth in ice, except those which were 



