310 
ANIMAL INTELLIGENCE, 
ground, which are thus wasted. A third species, the M . p^eoris 
of North America, has acquired instincts as perfect as those of 
the cuckoo, foi it never lays more than an egg in a foster-nest, 
so that the young bird is securely reared. Mr. Hudson is a 
strong disbeliever in evolution, but he appears to have been so 
much struck by the imperfect instincts of the Melothrus Ganari - 
ensis that he quotes my words, and asks, 4 Must we consider these 
habits not as especially endowed or created instincts, but as 
small consequences of one general law, namely transition ? 5 1 
Such are all the facts and considerations which I have 
to present with reference to the curious instinct in ques- 
tion. It will be seen that— with one doubtful or not suffi- 
ciently investigated exception, viz., that of cuckoos adapt- 
ing the colour of their eggs to that of the eggs of the 
foster-parents — there is nothing connected with these 
instincts that presents any difficulty to the theory of evo- 
lution. We may, perhaps, at first sight wonder why some 
counteracting instinct should not have been developed by 
the same agency in the birds which are liable to be thus 
duped ; but here we must remember that the deposition 
of a parasitic egg is, comparatively speaking, an exceed- 
ingly rare event, and therefore not one that is likely to 
lead to the development of a special instinct to meet it. 
General Intelligence . 
Under this heading I shall here, as in the case of this 
heading elsewhere, string together all the instances which 
I have met with, and which I deem trustworthy, of the 
display of unusually high intelligence in the class, family, 
order, or species of animals under consideration — the ob- 
ject of this heading in all cases being that of supplying, 
by the facts mentioned beneath it, a general idea of the 
upper limit of intelligence which is distinctive of each 
group of animals. 
That birds recognise their own images in mirrors as 
birds there can be no question. Houzeau, who records 
observations of his own in this connection with parrots, 3 
adds that dogs are more difficult to deceive by mirrors in 
1 Origin of Species , p. 215. 
2 Tom. I., p. 130. 
