2. As regards the assertion that species which are mimicked are either well-defended or unpalatable, this certainly does not hold good with regard to some at any rate of the coincidental resemblances among birds which we have pointed out; even if these pairs of similar species lived in the same country it would require considerable ingenuity to say why one should mimic the other.
3. As regards the argument that the inedible species of Ithomiinæ, etc., display only fifteen colours, while the less numerous edible Papilios display more than double this number of colours, we may draw attention to the fact that those birds which are most immune from attack are precisely those which display the smallest range as regards colour, e.g., hawks, owls, crows, gulls, storks, and cranes. As we have already submitted, no question of Müllerian association comes in here.
On the other hand, the eminently edible families of game-birds and ducks display great variety of colour, in the males at all events.
4. As regards the statement that although in many cases the mimetic resemblances extend to the minutest detail, they are not accompanied by any structural changes except such as assist in the production of a superficial likeness, we may refer to the case we have already cited of the New Zealand cuckoo, which, though it so closely copies an American hawk, is typically cuculine in structure. Here, of course, there can be no question of advantage to the “mimicking” cuckoo in the resemblances.
5. In answer to the argument that mimetic resemblance extends to form, attitude, and movement, as well as colour, and that deep-seated organs are affected only when the superficial resemblance is thereby intensified, we may draw attention to such cases as the following:—
(a) The harmless Indian Snake (Lycodon aulicus) is closely similar to the well-known Krait (Bungarus cœruleus), also Indian; but the resemblance extends to a structural detail which can hardly have mimetic value—namely, the harmless snake has long, fang-like front teeth, though these are unconnected with poison-glands. Animals which come into contact with the krait and its mimic are hardly likely to inspect their teeth.
(b) A considerable number of birds of the shrike group—known as Cuckoo-Shrikes (Campophaga)—closely resemble cuckoos in plumage; but even if they derive any benefit from mimicking birds which are credited with being mimics already, they cannot profit by the fact that the shafts of the rump-feathers in both groups are stiffened; this being a peculiarity which would not be perceptible until the bird was in the grasp of an aggressor.
(c) As a third case of coincidence we may refer to the tubercle in the nostril of the Brain-fever-bird (Hierococcyx varius), as a minute detail of hawk-like appearance, though not present in the particular species imitated.
6. The argument that mimetic resemblances are produced in the most diverse ways, but the result is uniform, loses much of its force when we consider the various methods by which short-tailed birds appear to have long caudal appendages.
In the peacock it is the upper tail coverts which are elongated; in the Stanley Crane (Tetrapteryx paradisea) it is the innermost or tertiary quills of wing; in one of the egrets some of the feathers of the upper back grow to a great length and form a train; in the Bird of Paradise (Paradisea apoda) the long flank plumes are commonly mistaken for the tail.