334 GEORG DUNCKER [NOVEMBER 
ences of age, sex, locality, in certain dimensions, and partly explaining 
them by selective processes [22, 23]. Further, he found a dimorphism 
of the females in the Naples race, which Giard [9] tried to explain 
by parasitic influences. In the meantime Thompson and Warren, 
inspired by Weldon, worked on variation and correlation in the 
dimensions of Palaemon serratus [15], Carcinus maenas [16], and 
Portunus depurator [17]. Warren first discovered the fact, afterwards 
several times confirmed, that the coefficients of correlation of homo- 
logous characters remain fairly constant not only within the form- 
units of the same, but also within those of allied but different species. 
Warren also was the first zoologist to follow Pearson’s improved method 
in analysing series statistically. Thompson demonstrated distinctly 
determined changes of mean value and index of variability in the 
characters of the same form-unit in different years, which result 
Weldon has investigated further, and has recently [24] considered as a 
proof of the reality of natural selection. 
While the leader of the English biological-statistical school is 
especially interested in the problem of natural selection, the North 
American school, led by C. B. Davenport, works especially on morpho- 
logical problems. First, Davenport in association with Bullard [6] 
investigated in a very rich material (4000 individuals) the influence 
of sex on the constants of variation and correlation. On Davenport's 
suggestion Brewster [1] and Field [8], the first in mammals, the 
second in insects, investigated the relation between the variability of 
certain characters and their systematic importance. The result tended 
to show that the two correspond. But the material basis of these 
investigations appears to me too small to settle this question definitely. 
Besides mathematical-statistical researches there have been pub- 
lished, since statistical methods came into vogue, some others of a non- 
analytical sort based upon large numbers of individuals. Among 
these I wish to call especial attention to Bumpus’ papers on variation 
and mutation in two very different species introduced from Europe to 
North America, the sparrow (Passe7’) [2], and the periwinkle (Littorina) 
[3]. In each of these instances the great increase of variability in 
the American forms, compared with the European ones, is remarkable. 
In Germany Heincke and I are still alone among zoologists in 
applying statistical methods to problems of variation. Heincke is 
chiefly interested in the existence of local races within the species, and 
one of his most important results is, I think, his method of determining 
the racial character of any given individual as well as its specific 
character [11]. Among botanists the number of fellow - workers 
increases every year. Besides foreign naturalists, H..de Vries and 
G. Verschaeffelt, who have published German papers, F. Ludwig has 
for several years been statistically investigating the law of Fibonacci 
in plants, while recently H. Voechting has published a splendid paper 
on abnormalities of flowers. There is a great advantage in botanical 
