250 THE ZOOLOGIST. 
caused solely by a continuous contemplation of the blue vault of 
heaven. 
In the case of the Cuckoo, it seems to me that matters are 
not much clearer than they were before. No suggestion with 
regard to the colour of the eggs of this bird has yet been made 
which is not full of difficulties. 
Dr. Romanes has remarked :—‘‘ We cannot imagine the Cuckoo 
to be able consciously to colour her egg during its formation in 
order to imitate the eggs among which she is about to lay it; nor 
can we suppose that, having laid an egg and observed its 
colouring, she then carries it to the nest of the bird whose eggs 
it most resembles.” Still the latter supposition is perhaps easier 
to believe than most of the suggestions, especially when we 
consider how very little is known as to birds and colour.* Any 
experiments in this direction would be sure to lead to interesting 
results, for birds are esthetically much more highly developed 
than mammals. 
Then there is Prof. Newton’s suggestion (‘ Animal Intelligence,’ 
p. 307), that “ there is very reasonable probability of each Cuckoo 
most commonly placing her eggs in the nest of the same bird, 
and of this habit being transmitted to her offspring.” 
This view seems to require— 
(1) A Cuckoo to have a favourite bird in whose nest to lay 
her eggs ; 
(2) An egg resembling the egg of that bird; and 
(8) Both these characteristics to be hereditary. 
And, apart from the criticisms put forward by Dr. Romanes on 
this hypothesis (‘Animal Intelligence,’ p. 308), would not this 
state of affairs, if true, result in considerably greater variations 
than are usually found among Cuckoos? Except one well 
recognized variety of the young bird, Cuckoos seem to vary very 
little. Would not several generations of Cuckoos all brought up 
by (say) Hedgesparrows, and fed to a great extent on Hedge- 
sparrows’ food, result in a well-marked variety, even though the 
difference between the food of a Hedgesparrow and (say) a Shrike 
were not sufficient to cause a strong difference to show itself 

* ‘Animal Intelligence,’ p. 307. This suggestion was made by Mr. 
Harting in an article on the Cuckoo published in ‘Science Gossip’ for May, 
1870, and subsequently reprinted in ‘ Sketches of Bird Life,’ 1883, 
