412 AN TOV EE, [DECEMBER 
character, or the variation in a character, as being “good for the 
species,” as having a “selective value,” when nothing definite is 
known. 
On the one side, therefore, we have “organs,” on the other side 
“species” ; and when we consider things as they naturally are, over 
all is the environment. Is it not possible, then, to find a method of 
grasping the mean? Between the organs and the species lies the 
most real of all, the individual—the unity of biology. If we could 
but understand the single life in its entirety through concentrating and 
testing on it all the conceptions of biology, we should know better 
the meaning of “change” — how it arises, and thence also the 
meaning of “ evolution.” 
This is the background of the task which Professor Heincke! set 
himself. After various trials at combining variations, and the making 
of formulas to represent groups and species, he advanced towards a 
method of determining, and a conception of the individual—not as an 
abstraction, but as something real and composed of organs, and forming 
one of many exactly equal under equal conditions. 
The method consists, not in the correlation of the variations of two 
or three characters, but in the correlation of the averages of as many 
characters as possible. If the variations of many characters are 
obtained, those of each character may be arranged about the centre 0, 
as in the ordinary mode of dealing with variations. Hence a system 
of groups of variations is obtained, each group representing the most 
probable distribution of the variations for that character, and the 
common centre representing the average of each group. If the varia- 
tions are then arranged in parallel columns they may be summed up 
and treated as if they were deviations from the common average at 0. 
In other words, the sum represents the distribution of the variations 
just as the ordinary arrangement of deviations about an average repre- 
sents their chance distribution. 
The assumption underlying this method” is that each group of 
variations conforms to the same “type” of probability, that of the 
“probability integral.” This assumption has already been challenged 
as if it invalidated the whole principle, but although it is not easy to 
say what correction should be made, a summation is certainly possible, 
and the warrant of its being near the truth is shown in the results. 
The law which arises from this summation holds good over all the 
individuals of a group under the same conditions. It gives the second 
proposition. 
2. The standard deviation of all the variations of the individuals 
when grouped about the common centre 0 is 1:18, and the probable 

1 «*Naturgeschichte des Herings,” Abhandl. des Deutsch. Scefisch.-Vereins, B. ii. H. 1, 
1898. 
2 A further assumption is that each character presents an independent series of 
variations. 
