152 
0)1 Honiotjiposis in E(j<js of the Common Tern 
Another relation suggested by Pearson * is that the cross horaotypic corre- 
lation of the characters x and y should on the average equal i (correlation of 
X and X + correlation of y and y) x (the organic correlation of x and y). It is 
clearly impossible from what has just been said to apply this to the cross 
homotyposis of ground colour and mottling. We can apply it to the five cases 
in which quantitative measuiements have been made. Table V gives the 
requisite data, the last two columns giving respectively the calculated and 
observed cross correlations. 
TABLE V. 
Cross Huiiwtypic Gurrelatiuns. 
Characters 
Direct Correlations 
Cross Correlation 
Orj^anic Correlation 
(1) and ('2) 
(1) 
m 
(1) and (1) 
(■2) and (2) 
Calculated 
Observed 
L 
B 
■4643 
•5176 
•2220 
•1090 
•0922 
L 
Gi 
•464.3 
•.5076 
•8804 
•4278 
•4229 
Gi 
Gu 
•5076 
•4621 
•5297 
•2568 
•2603 
B 
Gi 
•5176 
•5076 
•5216 
•2674 
•2530 
BjL 
•5076 
•5.537 
- •3832 
- -2033 
- ^2007 
When we compare the calculated and observed cross correlations, we see 
a striking agreement, or the theoiy that cross homotyposis is the product of 
direct homotyposis and the organic correlation of the characters under investi- 
gation holds very clo-ely for the egg of the Common Tern. 
The general results obtained are in good accord with those reached by previous 
observers, and the authors hope to investigate one or two doubtful points on 
fuller material this year. 
* Fhil. Trana. Vol. 197, A, p. 290. 
