220 



Part III.— Eighteenth Annual Report 



shown that the maturing of the reproductive organs hardly affects the 

 relative proportions of structures during the first year, but that later — if 

 400mm. be considered for the time being as the average-size of a group in 

 the second or later years of maturity — its effect is more clearly marked. 

 Hence, the withdrawal of a portion of their ordinary nourishment from 

 other parts of the body for the sake of the reproductive organs is the 

 direct physiological cause of the relative decrease in size of those parts. 

 And, on the other hand, we see that this relative decrease has a place in 

 the general fitness of things, because the balance of the organism is 

 thereby preserved. 



III. Race-variability. — After what has been said at the beginning of 

 the section on growth-variability, little further mention need be made of 

 the relationship of racial to the other forms of variability. It has been 

 shown that race-variability differs only in degree from the variability that 

 is present in a single group, and that the relationship between them may 

 be pictured by the aid of curves. If the variations of a large number of 

 specimens be plotted out in the form of a curve — the course of the curve 

 representing the "frequencies" accompanying each "variant," the 

 " variants " being marked off along an axis (abscissal axis) — then three 

 eventualities may arise. The curve may be quite continuous and have 

 only one maximal frequency (unimaximal curve), or, again, continuous but 

 with two or more maximal frequencies {multimaximal curve). This latter 

 form — if a certain distance, undefined by the author, lie between the 

 maxima — has been taken to represent " discontinuous variation " by 

 Bateson,* but it is clear that the word "discontinuous" is here misused. 

 The different forms of variability give rise to ranges of variation, which 

 grade into one another just as those of the external conditions in the 

 environment are supposed to do, and the continuity of the curve repre- 

 sents this continuous gradation. "Discontinuous variation" is present 

 when the two curves — i.e., the two ranges of variation — do not overlap at 

 all. Such would arise when the variabilities of two widely-separated 

 species — e.g., plaice and herring— were compared. 



To return to the consideration of the multimaximal continuous curve, 

 this may arise in the observed variations of a character of a group of 

 specimens in four different ways. Firstly, through sex-variability. It 

 has been shown in the section dealing with that subject how a group of 

 specimens, alike as regards age and region from which they came, may 

 show two distinct averages for the variations of a character by reason of 

 a difference between the sexes. If the sexes be taken together, therefore, 

 and the frequencies of the variants plotted along a curve, this curve may 

 present two maxima. Hence, when two di tie rent groups are to be 

 composed, it is necessary either to compare similar sexes only, or to 

 calculate, according to Galton's method, a sex-factor for each group so as 

 to eliminate the difference between the sexes. 



When sex-variability has been eliminated a multimaximal curve may 

 arise, secondly, through groioth-var lability. This appears in the changes 

 of the relative proportions of parts and organs during growth and maturity. 

 When two groups of specimens otherwise alike, but one about 300mm. in 

 length on the average, the other about 400mm., are compared, it has been 

 shown that the averages of the variations in certain characters are not the 

 same, and we may thus have a multimaximal curve when these variations 

 are arranged in this form. Hence, if two groups of specimens are 

 examined for racial differences, it is necessary either to compare the 

 specimens of the same size in the two groups, or, as above, to calculate 

 the growth-coirrection or factor so as to bring all the specimens to the same 

 size. 



* Bateson, W. : "Materials for the Study of Variation," Introduction ; 1894. 



