A Cooperative Stud}/ 
333 
speculating on the source of this marked seasonal change in size homotyposis. 
One point, however, we can investigate, namely, whether piginentation homoty- 
posis has or has not kept pace with size homotyposis. 
With this aim in view the direct homotyposis has been worked out between 
mottling of one egg and mottling of a second in the same clutch, and between 
ground colour of one egg and ground colour of a second in the same clutch. 
Further the cross-homotvposis has been determined between the mottling of one 
egg and the ground colour of a second in the clutch. The fundamental difficulty 
here lies in the treatment of the ' values ' of the ground colour. We cannot 
separate green eggs from brown, because of the occasional appearance of mixed 
colour clutches. Nor would it be reasonable to work with contingency on a 
20 X 20 category table. We have accordingly been compelled to pool green and 
brown eggs, when they have the same ' value ' on our colour scale. This at any 
rate renders our pre.sont results comparable with those uf 1913. But until we 
know more of the mechanism of egg piginentation it is impossible to assert that 
equal ' values ' in brown and green ground colours are what we should anticipate 
as a result of individuality working occasionally with one and occasionally with 
another pigment. The homotyposis piginentation tables ai'e given as Tables 
R, S, and T at the end of this paper. In actiuxUy determining the contingency we 
have clubbed d and e in the mottling together, and Ay and A.>, and B.^, 
Ci and Oa, etc. in the value of the ground colour, thus reaching 8 x 8, 10 x 10 and 
10 X 8 contingency tables. These have then been corrected for number of cells 
and for class-index correction. The class-index correction for mottling is '9531, 
and for value of ground colour •9848. 
We consider first the cross-homotyposis of ground colour and mottling. The 
coefficient of mean square contingency on the supposition that there is no asso- 
ciation between value of ground colour in one egg and mottling in a second 
would be 
= -1992 ± -0169. 
The corrected actual coefficient of mean square contingency is 
C4 = -1479, 
which is less than the mean square contingency coefficient for no association. 
Accordingly there is no cross-homotyposis between mottling and ground colour, 
and there should not be if our view be correct that the organic relationship in 
the same egg is zero (see p. 328). 
The value found for the 1913 data was 
a = -3989 + -0379, 
and was spoken for as significant. But the fact was overlooked that 
C, = -3169 ± -0451, 
so that G-i is less than twice the probable error greater than G.,, and may well not 
be significant. This conclusion is confirmed by the considei'ati(jn that the organic 
correlation of mottling and ground colour was really insignificant in 1913, and 
