THE VARIATION, EACES AND MIGRATIONS OF THE MACKEREL. 241 



verse Bars, i.e., whether straight, > shaped, or wavy; and whether 

 regular, fairly regular, rather regular, or irregular. 



8. The Continuity or Degree of Discontinuity of the black longitu- 

 dinal Streak which is present in most mature fishes below the lateral 

 line. I call this character the " Lateral Streak." 



9. The extent and character of the Dusky Markings which are 

 frequently found in mature fishes below the Lateral Streak, especially 

 in the anterior half or third of the body length. These markings, when 

 well developed, have the form of a fine zigzag tracery, but they are often 

 diffuse and blurred. I call this character the " Sublateral Tracery." 



10. The Abundance and Distribution of small irregular dusky Spots, 

 frequently found on the posterior part of the abdominal region, and 

 scattered over and among the Transverse Bars of the Dorsolateral Area. 

 They are to be sharply distinguished from the round black Spots which 

 I have termed "Dorsolateral Intermediate Spots." The pigment of 

 these latter is a deep black, and it is situated at a lower level in the 

 tissues than the pigment of the irregular "Dusky Spots." Moreover, 

 the Dorsolateral Spots are invariably situated hetween two adjacent 

 Transverse Bars, of which, in a morphological sense, they are undoubt- 

 edly discontinuous modifications. The Dorsolateral Spots are independent 

 of the growth of the fish, being as frequent in small fish as in large, 

 but the " Dusky Spots " appear to make their first appearance about 

 the time of maturity. 



11. The Extent of a black longitudinal Connecting Streak which 

 connects the ventral ends of the Transverse Bars. The Connecting 

 Streak is usually confined to the posterior quarter or third of the 

 body-length, but occasionally extends further forwards, and in rare 

 instances traverses the whole length of the body, intersecting the 

 lateral line at an acute angle. In such cases the "Lateral Streak" is 

 frequently ill-developed. 



Of these accessory characters, only the first (No. 7 — the Shape of 

 the Transverse Bars) has been considered in the present report, 

 owing to its suggested bearings on the question of secondary sexual 

 peculiarities. 



The data acquired in regard to the variation of the remaining 

 accessory characters are not discussed in the present report, although I 

 hope to make use of them on a future occasion. My reasons for 

 omitting them are chiefly that some of the characters (Xos. 8, 9, and 

 apparently 10) were found to arise rather late in life, about the time of 

 maturity ; and as the exact size at which they make their appearance is 

 itself subject to variations, it was considered inadvisable to introduce 

 such characters into a discussion of racial peculiarities until the causes 

 which determine their appearance have been more definitely ascertained. 



