Moreover, the investigation of a smaller area may also bring to light points of difficulty. In Ceylon, for example, _P. polytes_ is common up to several thousand feet, while _P. hector_ is rare at half the height to which _polytes_ ascends. Nevertheless the H form of female is relatively just as abundant up-country where _hector_ is rarely found as it is low down where _hector_ is plentiful[41]. On the other hand, _P. aristolochiae_ may be exceedingly abundant at altitudes where _hector_ is scarce. Yet the A form of _polytes_ is no more relatively abundant {80} here than elsewhere on the island. All over Ceylon, in fact, the relative proportions of the three forms of female appear to be the same, quite irrespective of the abundance or scarcity of either of the models. As, however, we shall have to return to this point later, we may leave it for the moment to consider other features of this case of _P. polytes_. In collections of insects from India or Ceylon it is not unusual to find specimens of the A form of female of _polytes_ placed with _P. aristolochiae_, and the H form with _P. hector_. When the insects are old and faded and pinned out on cork the mistake is a very natural one. But after all the enemies of _polytes_ do not hunt it in corked cabinets, and any estimation of resemblance to be of use to us must be based upon the living insects. Are the resemblances of the mimics to the models when alive so close that they might be expected to deceive such enemies[42] as prey upon them and have no difficulty in distinguishing the male form of _polytes_ from _P. aristolochiae_ or _P. hector_? To answer for a bird is a hazardous undertaking. We know so little of the bird's perceptive faculties whether of taste or sight. But on general grounds, from the specialization of their visual apparatus, it is probable that the sense of sight is keen, though whether the colour sense is the same as our own is doubtful[43]. On the other hand, the olfactory apparatus {81} is relatively poorly developed in birds, and from this we can only argue that the senses of smell and taste are not especially acute. Really we can do little more than to describe how these mimetic resemblances appear to our own senses, and to infer that they do not appear very different to the bird. If there is any difference in keenness of perception we shall probably not be far wrong in presuming that the advantage rests with the bird. After all if there is any truth in the theory of mimicry the bird has to depend largely upon its keenness of sight in making its living, at any rate if that living is to be a palatable one. If natural selection can bring about these close resemblances among butterflies it must certainly be supposed to be capable of bringing the bird's powers of vision to a high pitch of excellence.