W. Ho WAN, K. M. Parker and J. Bell 149 
TABLE III. 
Observed and Ctdculated Longitadinal Girths. 
Calculated Girth 
Dili'erence 
Observed 
Number 
(jrll in 
(ii) 
(i) 
Ai 
1 
11-40 
11-14 
11-20 
+ -26 
+ ■20 
2 
11-65 
11-83 
11-74 
- -18 
- -09 
12-10 
12-24 
12-07 
- -14 
+ -03 
\ 
10-80 
11-46 
10-84 
- -66 
-•04 
5 
11-70 
11-23 
11-31 
+ -47 
+ -39 
6 
11-20 
•117 
7 
12-15 
13-19 
12-31 
-1-04 
--16 
" {'■) 
1 1 -20 
11-19 
11-27 
+ -01 
- -07 
8{n) 
11-30 
11-09 
11-27 
+ -21 
+ •03 
9 (i) 
11-50 
11-44 
11-61 
+ -06 
- •ll 
9(ii) 
11-40 
11-36 
11-45 
+ -04 
- -05 
10 
11-50 
11-52 
11-61 
- -02 
-•11 
11 
11-80 
1 1 -55 
11-72 
+ -25 
+ •08 
12 
11-90 
11-62 
11-74 
+ -28 
+ -16 
IS (i) 
11-10 
11-01 
10-94 
+ -09 
+ •16 
13 (ii) 
10-80 
10-75 
10-78 
+ -05 
+ •02 
IS (iii) 
11-70 
11-45 
11-55 
+ -25 
+ •15 
Root mean 
-354 
-146 
square A 
i 
To judge by this small sample we obtain only increased inaccuracy by taking 
the more complicated formula. We shall only make an error of about 1^ mm. if 
we calculate the longitudinal girth from 
Gi = 1-2701 B + 1-6415 L + -8224, 
and for the egg of the Common Tern at least this is a convenient formula for 
verifying measurements in the field. 
The remaining correlations indicate sensible correlations, but these correlations 
might well be substantially higher had a better scale of mottling been adopted 
ab initio. In the first place we see that the mottling and the ground colour 
are sensibly correlated, and the deeper the ground colour the more intense is 
the mottling*. 
We have already seen (p. 146) that for eggs of the same clutch the broader 
lias less intensity of ground colour and more meagre mottling. This is true 
for the eggs of the Common Tern in general, although it is probable that a better 
classification of mottling would bring out more marked correlations. The 
■" This might probably be asserted interracially as well as intraracially, compare for examijle the 
swallow with the skylark, the lapwing with the ringed plover, etc. 
