312 
On the Nt\^t and E<jgs of the Common Tern 
character of their eggs. If the egg in shape, colour-vahie and mottling be related 
to the individual nest, it is hardly conceivable that a hen, especially when a young 
bird, can d priori appreciate what the type of her egg is likely to be and prepare 
the corresponding protective nest accordingly. Such an instinct would be con- 
ceivable in the case of a species with more uniform eggs and building a specific 
type of nest ; it is hard to conceive it possible in the case of such a wide colouring 
and mottling range as we find in the common tern. The alternative is to suppose 
a considerable variety of tern gentes, who like the suggested cuckoo gentes select 
a particular environment for their eggs. Such a suggestion is not without 
difficulty; it involves mating within the gots, or a transmission of the egg colour- 
ing mechanism through the female only. To accept the latter is not consonant 
with our experience that sexual characters of the female are transmitted through the 
male, i.e. the fei'tility of the mare and the character of a cow's milk are correlated 
with the like characteristics in their paternal grandniothers. It is conceivable that 
the pigmentation may vary to some extent with the immediate food supply. In 
this case green and brown eggs of the same sliape and size within the same 
clutch might be more readily accounted for than by the hypothesis of two hens of 
different gentes using the same nest*. It might also admit of the hen having 
some inkling of the character of her forthcoming eggs, if the nest be made before- 
hand. Besides this it would free us from any hypothesis as to tern gentes. 
Thus far we have written as if the protective colouring of eggs was a demon- 
strated phenomenon. It is highly probable in the case of many species building 
specific nests in specific environments. Can it be asserted of the common tern ? 
If not, elaborate and most varied colouring and mottling would appear to be 
physiological, and originate before they attain protective character. In other words 
egg patterns have been specially selected for protective purposes, but did not 
originate in the survival of the better protected. 
It will be remembered that we have divided our nests into the unelaborated 
nests, i.e. nests with no material, and with no hole, or merely a hole in the ground, 
and elaborated nests or nests formed by a hole and with accumulated material. 
We shall denote these by S and 0, i.e. simple and complexf. We will consider 
first absolute size as measured by the longitudinal girth, Gi. 
The following table gives the data. The mean of the *S'-nest eggs is 11'5.56 as 
against 11"373 for the total population. The correlation found by the biserial r 
method was 
,•= + •0(385 ± -0322. 
* Clutch 0, figured in Plate III, shows three eggs practically identical in shape and size yet of very 
different ground colour. Since the size is quite abnormal — being the smallest found in 1914 — one can 
hardly believe that three birds laid three such epgs in one and the same nest ! Again in the Psamma 
nest referred to in the ftn. p. 308, the three eggs were laid on three successive days ; two eggs were 
alike in colour, but the third completely different. 
t Actually of course every degree of elaboration can occur with a hole and every degree of accumu- 
lation of material. Thus although we have only two categories these cover practically continuous 
grades of elaboration and justify the use of biserial r method of determining the association. 
