362 FISHES 



which as a species is found on the coasts of both Europe and 

 North America. The chief characters which he examined were 

 the number of transverse black bars on the sides, the number of 

 spots between the bars, the number of dorsal finlets, and the 

 number of fin-rays in the two dorsal fins. In all these char- 

 acters there was a range of variation, and although in samples 

 from different regions the ranges overlapped, the investigator 

 obtained evidence that the " mode " or most frequent variation 

 in American fish was different from that in European samples, 

 and further that there was a similar but smaller difference be- 

 tween Irish mackerel and those from the North Sea and Eng- 

 lish Channel. The American mackerel showed the highest 

 averages in the following characters: (i) the number of trans- 

 verse bars, (2) the number of spots, (3) the number of dorsal 

 finlets ; while they yielded the lowest averages in the rays of 

 both dorsal fins. Mr. Garstang draws the conclusion that al- 

 though the mackerel is considered a migratory fish, it does not 

 migrate to so great an extent as formerly supposed ; that it 

 certainly does not cross the Atlantic. This is a necessary con- 

 clusion with regard to the adult fish, but it is still an open 

 question whether the differences are hereditary or whether 

 European mackerel, if reared in American waters, would de- 

 velop the characters of the American fish. It also follows that 

 the fish of the south and west of Ireland do not as a rule 

 migrate into the English Channel or North Sea and vice versa. 

 Similar statistical studies of continuous variation have been 

 made by Professor Eigenmann on Leuciscus balteatus, a. species 

 living in the Columbia and Frazer Rivers of western North 

 America and belonging to the same genus as our own minnow, 

 roach, chub, and dace. He found a great range of variation, 

 especially in the number of rays in the ventral fin. In all the fresh- 

 water fishes of the Pacific slope of North America there is a much 

 greater range of variation than on the Atlantic slope, both in 

 the characters of allied species and the individuals of a single 

 species. In the case of Leuciscus balteatus Eigenmann found 

 that every locality had a variety peculiar to itself, each different 

 in the average number and in the curve of variation of the 

 ventral rays. For example, in the Frazer River seventy-nine 

 specimens were collected in water affected by the highest tides 

 of the sea, fifty-nine at an elevation of 1300 feet in the upper 



