8) 
believers in natural selection may properly be asked to bring 
evidence of the existence of a struggle in which the high 
elaboration of the instincts in question is a defence. ‘There is 
no difficulty in meeting the challenge, for specially directed 
observation at once reveals the existence of a keen struggle in 
which the concealment of the cocoon is the criterion of life or 
death. 
My attention was first directed to this particular aspect of 
the struggle for existence in insects, on April 12, 1893, when 
I found on the bark of Populus nigra, near Yoxford, Suffolk, 
a cocoon of Dicranura bifida which had been opened by some 
enemy, and the pupa removed. The observation is, I believe, 
a common one, in fact Commander Walker and Mr. Holland 
inform me that it is usually difficult to find cocoons of this 
species which have not been thus attacked. Nevertheless, for 
the sake of those who have not had the experience, I think it 
is worth while to re-describe the evidence which certainly 
justifies us in inferring that ‘an enemy hath done this.” 
“The edges of the opening were still brown and fresh, as 
was the interior of the cocoon; and the larval skin remained fresh 
and untouched inside. The opening was in the middle of the 
exposed surface and not at one end, as it is when the moth 
emerges. Besides, the cocoon had been opened and cracked by 
a blow from some hard object, such as a bird’s beak, and the 
sharp irregular margins were quite different from those of the 
natural opening made by the moth, doubtless by means of a 
corrosive fluid, as in the allied species, Dicranwra vinula, which 
Mr. O. H. Latter has recently shown to secrete caustic potash 
for this purpose. Furthermore, the moth emerges far later in 
the year, and, had it emerged at an exceptional time, the empty 
pupal skin would have been left behind in the cocoon. We 
may therefore safely assume that the opening was the work of 
an enemy, and, as the cocoon was five feet from the ground, it 
was probably due to some tree-creeping, bark-exploring species 
of bird. . . . It is probable that the attention of the enemy 
is directed to any cocoon-like object by the sense of sight, and 
that the object is then tapped, and, if found to be hollow, 
opened and the pupa devoured.” * 
* “The enemies of Lepidopterous pupe enclosed in bark-formed 
cocoons,” —‘‘ Science,” xxiii, 1894, p. 62. The date of the observation is 
