ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 663 



differences which would on Heincke's method admit of their separation 

 into races were found. Between the mackerel caught in the Clyde, at 

 Barra and Stornoway, and off Aberdeen, the differences in the lengths 

 of the head, skullj and pectoral fin may with some probability be granted 

 lacial distinction. The shorter length of head and skull, in which the 

 Clyde and Barra and Stornoway lots more closely resemble one another, 

 separate them slightly from the Aberdeen collection, and in respect to 

 a shorter pectoral fin the Aberdeen and Barra and Stornoway fishes are 

 separated by a small interval from the ( 'lyde individuals. With regard 

 to the other characters, the author considers that the evidence docs not 

 prove them of racial distinction. 



Natural History of the Plaice.* — Mr. H. M. Kyle finds that the 

 average size at first maturity for the plaice of the southerly North Sea 

 lies between 13 and 14 in. for the female and between 10 and 11 in. 

 for the male. In the northerly North Sea plaice this average is for 

 females about 15 ■ 5 in., for males about 12 ■ 5 in. The difference between 

 the sizes of the sexes at this period may correspond to a year's growth. 

 Following the example of Heincke, he applies the mathematical method 

 to the problems of sex-, growth-, and race-variability. Secondary sexual 

 differences have not been found in vertebrae, fin-rays, body-height, nor 

 tail. The skull-dimensions, length, breadth, and depth are slightly 

 greater in the female than in the male, and this is probably connected 

 with the mass and position of the reproductive organs, which arc larger 

 and placed more posteriorly than in the male. In a group of individuals, 

 similar in size and sex, there is a range of variation in number of 

 vertebras and fin-rays, which is probably due to surrounding physical and 

 chemical conditions only. These structures do not vary with growth, 

 but are fixed at the earliest stages. The body-height and length of tail 

 do not alter relatively to the body-length during growth, but there is a 

 relative decrease of skull-length and breadth. As to skull-depth, this 

 dimension does not alter relatively to the skull-length. As to race 

 variability, it is shown that the North Sea plaice are divided into at least 

 two groups by distinct differences in structure. The northern forms 

 have greater body-height, they are rounder more massive fish, while the 

 southern forms are more slender but longer. The changes in the relative 

 proportions of structures due to sex, growth, or race, probably do not 

 disturb the " balance of organs." If this balance is constant for the 

 species, these alterations in the relative proportions of structures indicate 

 the various possible combinations of structures and organs which may 

 arise from the specific variability of the organism. 



Flat-Fishes.f — Mr. H. M. Kyle gives a classification of the Hetero- 

 somata. The family groups are, with slight modifications, taken from 

 the recent work of Jordan and Evermann4 As important characters 

 distinguishing the various sub-families he makes use of: — (1) the posi- 

 tion of the nasal organ of the under or blind side relative to the anterior 

 extremity of the dorsal fin ; (2) the form and structure of the olfactory 

 epithelium. The geographical distribution and affinities of the various 

 sub-families arc discussed. 



* Ann. Eep. Fishery Board for Scotland, xviii. (1900) pp. 1SH-241 (2 pis.). 



+ Tom. oit., pp. 3:J5-G9 (2 pis.). 



% 'The Fishes of North and Middle America,' Washington, 1S9S. 



