The Brain-fever Bird 
operate on it. It is therefore absurd to look upon 
natural selection as the direct cause of the origin 
of the likeness. When once a certain degree of 
resemblance has risen, it is quite likely that in 
some cases natural selection has strengthened 
the likeness. 
The second great objection to the Neo- 
Darwinian explanation of the phenomenon 
known as mimicry is that in many cases the 
resemblance is unnecessarily exact. Even as 
we saw how the Kallimas, or dead-leaf butter- 
flies, carried their resemblance to dead leaves 
to such an extent as to make it appear probable 
that factors other than natural selection have had 
a share in its production, so do we see in certain 
cases of mimetic resemblance an unnecessarily 
faithful likeness. 
The common Hawk Cuckoo of India (//zero- 
coccyx varius) furnishes an example of this: 
“ The brain-fever bird,” writes Finn, on page 58 
of Ornithological and Other Odditzes, “is the 
most wonderful feather copy of the Indian 
Sparrow-hawk or Shikra (Astur badius). All the 
markings in the hawk are reproduced in the 
cuckoo, which is also of about the same size, and 
of similar proportions in the matter of tail and 
wing; and both hawk and cuckoo having a first 
plumage quite different from the one they assume 
when adult, the resemblance extends to that too. 
Moreover, their flight is so much the same that 
235 
