DOES THE CUCKOO INCUBATE ? 221 
from it the two Cuckoo’s eggs, a reddish brown one, and a very 
small one which the female Cuckoo had pushed aside. After 
Herr M. had repeatedly observed the Cuckoo feeding her young 
one with little green caterpillars at short intervals (three times in 
ten minutes), he found on June 10th that the young Cuckoo had 
left the nest, but it was still close by, and was being fed by its 
parent. 
This shortly is the gist of Herr Muller’s “ personal observa- 
tions.” Before discussing the matter further, I must express my 
astonishment that Herr M. has overlooked what would have 
afforded a better explanation, and lent more probability to his 
narrative. To begin with, I may mention as a most striking fact 
that he did not keep the unincubated eggs and egg-shells. Most 
certainly several of our ornithologists—I need only mention Dr. 
Baldamus, Dr. Kutter, and Herr W. von Nathusius—would have 
been able, by examining the egg-shells, to prove whether the eggs 
which were pushed aside were Cuckoos’ eggs or not. In such a 
remarkable case no naturalist would throw a fragment of an egg 
away. For my part I carefully preserve such specimens in my 
collection. I have, for example, fragments to show that the 
Cuckoo invariably lays similar eggs. Besides, fragments of 
Cuckoos’ eggs are in much request for examination of the shell. 
Returning to the discussion, I may observe that Herr M. 
is frequently in opposition with ascertained fact, and insists on 
untenable views. Thus he allows his Cuckoo to lay and sit on 
three eggs of a different colour and size, and avers in effect that 
one and the same Cuckoo laid them. This is not accurate; 
for one and the same female, as is the case with other birds, 
always lays similar eggs, as I am clearly able to prove. Now if 
all three eggs had really been Cuckoos’ eggs (and they were 
not recognized as such by Herr M. on his discovery of the nest), 
they must have been laid by three different Cuckoos, which is 
absurd. Therefore the Cuckoo did not sit on its own eggs, or at 
most on only one of them. In my opinion, however, these three 
eggs could not have been Cuckoos’ eggs at all,—certainly not the 
small one, as shown by its small size, its colour, and especially 
by its brittleness. Cuckoos’ eggs are, in fact, not brittle, but 
uncommonly firm and hard. Who would take for an egg of the 
Cuckoo that which is thus described by the observer ?—‘ The 
most curious egg was the third, which was quite different from 
