. : A Cooperative Study 315 
The mean index for the rougher nest was 72'530 and for the general 2)0])u- 
lation 7l"752. We find for the correlation : 
r = - -1372 ± -0319, 
a value greater than in the case of either length or breadth, the less elaborated 
nests having the rounder egg. 
We now took G = B- x L as a rough measure of the volume of the egg and 
found : 
r = - -0223 ± -0322, 
or r is sensibly zero. In other words there is no relation of volume of egg to the 
type of the nest. Since we might suppose the younger bird to lay smaller eggs, 
or at any rate less broad eggs, the solution of the simple nests being due to 
young birds finds no confirmation in our analysis : it is the shape of the egg 
rather than its size which is associated with its environment. In order to test 
this further the lower portion of the axis L — \B and the Second Index of 
Ovality*, 100 (Z — \B)IB, were correlated with the type of nest. 
They gave respectively : 
r = + -1233 ±-0319, 
and r = + -1492 ± -0318. 
In other words the greater the extension below the hemisphere and the greater 
the ovality the more likely the nest to be elaborated. Thus we see that the rotund 
egg is more characteristic of the careless nest. It is conceivable that the rounder 
the egg the less likely it is to catch the eye when laid amid small pebbles and 
shingle. We next turn to investigate the association of colour and mottling with 
type of nest. First we inquire as to the simple relation of green and brown to 
the nest. Here we cannot go further than a fourfold table : 
* The relative advantage of 02 = 100 (L - and Oj = 1007:>V(L - i B) consists solely in the ovaloid 
character of the egg increasing as <)■, increases, while it decreases as Oi increases. Either may really 
be used indifferently if this be borne iu mind. 
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