192 



LOWER VERTEBRATES. 



The common mackerel of commerce, Scomber scombrus, is destitute of an air- 

 bladder, and the upper surface of the head is almost uniformly dark and destitute of 

 any transparent area ; the scales are all minute, and no corselet is developed ; and the 

 first dorsal has normally twelve spines ; the color above is a lustrous dark blue, trav- 

 ersed by about thirty-five undulating blackish bands or streaks, and below it is silvery; 

 the pectorals are dark at the base. The great importance of this fish justifies a more 

 detailed consideration than we have been able to give to other species, and for our 

 information we will be largely indebted to recent reisorts by Goode, Collins, and Earle, 

 from which we will take freely, with as little change of language as is necessary. 



Mackerel, when well grown, are about seventeen or eighteen inches long, although 

 sometimes they attain a larger size, perhaps nineteen or nineteen and a half inches 



long, or, very rarely, even 

 somewhat more. The 

 .^^^^ size varies however. A 



'number one' mackerel, 

 accoi'ding to the Massa- 

 chusetts inspection laws, 

 measures thirteen inches 

 from the tip of the snout 



Fig. 114.— Scomber scombrus, mackerel. tO the end of the Caudal 



fin. " The average length 

 from year to year, for the whole coast, is probably not far from twelve inches," with a 

 weight of twelve to sixteen ounces. 



In the American seas, the range of the mackerel extends from the neighborhood 

 of Cape Hatteras, northward to Labrador and Newfoundland. In the early spring, 

 as well as in the late summer and fall months, they may be found in the latitude of 

 North Carolin;x, while in the summer months they abound off the coasts of the middle 

 states and New England, and esijecially in the Gulf of St. Lawrence. They may be 

 also found on the coast of Labrador, though there is no evidence that they ordinarily 

 frequent the waters north of the Strait of Belle Isle, and it has been asserted that they 

 visit northern Labrador only in seasons i-emarkable for the prevalence of westerly 

 winds, and that in others they do not go so far northward. They neither visit Hud- 

 son Bay nor the coast of Greenland. On the eastern side of the Atlantic the 

 species inhabits the entire length of the Norwegian coast, from the North Cape to 

 Christiania Fjord, and it also occurs on the south coast of Sweden, in the Baltic, the 

 German Ocean, and the English Channel, as well as almost everywhere round the 

 British Islands, and southward to the Mediterranean, where it abounds, especially in 

 the Adriatic Gulf. In short, the mackerel must be considered as a fish not addicted 

 to wide wanderings in the ocean and with a normal range, limited in the western 

 Atlantic between latitudes 35° and 56°, and in the eastern Atlantic between 36° and 

 71°. The species is, however, quite erratic in its appearance along the coast, and its 

 movements appear to be determined by both temperature and food ; primarily by 

 temperature, and secondarily by the animals constituting its food, but, inasmuch as 

 the distribution of the latter is determined chiefly by temperature, the factor is really 

 mainly thermometric. 



The migrations of the mackerel, according to Mr. Goode, are believed to be car- 

 ried on in connection with another kind of migration, which he calls " bathic migra- 

 tion," and which consists in " a movement, at the approach of cold weather, into the 



