98 Proceedings of the Royal Physical Society. 
Cuculus canorus is tending to break up into a number of sub-species, 
each with its own particular habits in respect of selecting a foster 
parent” (p. 363). 
It is not my intention in the present paper to criticise this conclusion on 
the evidence submitted in Mr Latter’s paper, further than to remark that there 
appears to be an arithmetical slip in his determination of the significance of 
the difference between the mean lengths of the total Cuckoo eggs treated of 
and the mean length for the “Sedge-warbler-cuckoo” group. Besides, the 
standard deviation of sampling used is not that of the difference between a 
general mean and a local mean, which is the difference Latter considers. 
Even when the correct formula is used it does not render distinctly significant 
the difference in the “Sedge-warbler-cuckoo.” 
The proposition here submitted, based upon the coloration of the Cuckoo’s 
egg, is that the assumed habit on the part of the Cuckoo of adhering to a 
particular species of foster bird is not in general agreement with fact. 
Further, we have here confirmed two generally recognised facts :— 
(1) A considerable variability of colour in Cuckoos’ eggs in general ; 
(2) A marked uniformity of colour of the egg of the individual bird. 
An examination of the 300 Cuckoo eggs in the Fenton collection reveals 
the fact that in this species there is a wide range of variation as regards egg 
coloration. This agrees with the observation of other investigators, ¢.9. 
Newton (4), Baldamus (1), Herrick (2). Herrick states: “When taken at 
random they are very variable in colour, ranging from blue, or blue-green, 
through speckled blue, brown, mottled or marbled brown, and grey to nearly 
plain white.” There is also general agreement upon the question of the 
uniformity in coloration of the eggs of the individual Cuckoo. Newton 
writes: “ It is unquestionable that whatever variation there may be among 
the eggs laid by different individuals of the same species, there is a strong 
family likeness between the eggs laid by the same individual, even at the 
interval of many years” (D. of B., p. 123). Herrick states: “The same 
Cuckoo always lays eggs of similar colour, colour pattern, size and form in a 
single season, and probably during life. According to Baldamus this has 
been proved to hold true in one case for three successive years. If two or 
three Cuckoos’ eggs are found in the same nest, they are supposed to belong 
to different birds, and no case is known where such eggs were similarly 
coloured.” 
An examination of the Cuckoos’ eggs in the Fenton Collection, grouped 
according to locality and date of taking, shows the presence, in numerous 
instances, of sets of eggs of strikingly uniform coloration. No other 
