ON H0M0TYP08IS AND ALLIED CHAEACTEES 
IN EGGS OF THE COMMON TEEN 
By WILLIAM ROWAN, K. M. PARKER, B.Sc, and JULIA BELL, M.A. 
(1) Origin of the material and method of measurement. 
The settlement of Common Terns, which provided material for the present 
work, is one of old establishment on Blakeney Point, Norfolk. This is a shingle 
spit of some 8 miles in length on the north coast of Norfolk, about 12 miles 
west of Cromer. The colony is situated on the very end of the point, with 
water on three sides. Here the spit is a combination of dunes, salt marsh and 
shingle, and for the most part the nests are found on the open shingle on the 
seaward side of the dunes. Nests are plentiful in the embryo dunes in some 
years, though this year (1913) none were found there. The colony was more 
scattered than usual and covered the greater part of a mile of sea front. To 
avoid missing any clutches, Miss K. M. Parker, B.Sc, and Mr William Rowan 
divided the nesting area into suitable well marked plots and worked these one 
after another. Each of these again were worked in strips, till a patch was com- 
pleted, when the workers moved on to a remote one, to give the birds a chance of 
settling down again. After measurement each egg was numbered with indelible 
ink, so that any one egg was never measured twice. In all 203 clutches were 
handled. 
(2) Reduction of the material. 
The principal part of the work of tabling and reduction was carried out by 
Julia Bell*. The characters dealt with were: 
(i) 
Length of Egg ........ 
L 
(ii) 
Breadth of Egg, maximum value . . . . . 
B 
(iii) 
Lateral Girth at section with maximum breadths 
Go 
(iv) 
Longitudinal Girth ........ 
Gi 
(V) 
Length-Breadth Index ....... 
BjL 
(vi) 
Mottling, as determined from a scale of typical eggs 
M 
(vii) 
Ground Colour, as determined from a tint scale 
C 
* The authors have to thank Miss B. M. Cave for certain tables and their correlation coefficients. 
The Editor is responsible for the actual wording of this paper. 
