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aware of the importance of the observation of the tongue ; but as the bill was so short and the tubular tongue not required, there can be little doubt that the organ was, at that carly stage of growth, short and flat, as it is in the birds most nearly allied to them.

Differences between Sun-birds and Ilumming-birds. - In respect of all the essential and deep-seated points of structure, which have been shown to offer such remarkable similarities between the swifts and the humming-birds, the sun-birds of the Eastern hemisphere differ totally from the latter, while they agree with the passerine birds generally, or more particularly with the creepers and honey-suckers. They have a deeply-notched sternum; they have twelve tail-feathers in place of ten ; they have nineteen quills in place of sixteon; and the first quill instead of being the longest is the very shortest of all, while the wings are short and round, instead of being excessively long anı pointed; their plumage is arranged differently; and their feet are long and strong, instead of being excessively short and weak. There remain only the superficial characters of small size and brilliant metallic colours to assimilate them with the humming-birds, and one structural feature-a tubular and somewhat extensile tongue. This, however, is a strictly adaptive character, the sun-birils feeding on small insects and the nectar of flowers, just as do the humming-birds ; and it is a remarkable instance of a highly peculiar modlification of an organ occurring independently in two widely-separate groups. In the sun-birds the hyoid or tongue-muscles do not extend so completely over the head as they do in the humming-birds, so

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that the tongue is less extensible ; but it is constructed in exactly the same way by the inrolling of the two lamine of which it is composed.

The tubular tongue of the sun-birds is a special laptive modification acquired within the family itself, and not inherited from a remote ancestral form. This is shown by the amount of variation this organ exhibits in different members of the family. It is most highly developed in the Arachnotheræ, or spiderhunters, of Asia, which are sun-birds without any metallic or other brilliant colouring. These have the longest bills and tongues, and the most developed hyoid muscles; they hunt much about the blossoms of palmtrees, and may frequently be seen probing the flowers while fluttering clumsily in the air, just as if they had seen and attempted to imitate the aërial gambols of the American humming-birds. The true metallic sunbirls generally cling about the flowers with their strong feet; and they feed chiefly on minute hard insects, as do many humming-birds. There is, however, one species (Chalcoparia phenicotis) always classed as a sun-bird, which «liffers entirely from the rest of the species in having the tongue flat, horny, and forked at the tip; and its food scems to differ correspondingly, for small caterpillars were found in its stomach. More remotely allied, but yet belonging to the same family, are the little flower-peckers of the genus Diceum, which have a short bill and a tongue twice split at the end ; and these feed on small fruits, and perhaps on buds and on the pollen of flowers. The little white-eyes (Zosterops), which are probably allied to the last, eat soft fruits and minute insects.

Here then we have an extensive group of birds, considerably varied in external form, yet un loubtedly closely allied to cach other, one division of which is specially adapted to feed on the j: secreted by flowers and the minute insects that occur in them; and these alone have a lengthened bill and double tubular tongue, just as in the humming-birds. · We can harılly have a more striking example of the necessity of discriminating between adaptive and purely structural characters. The same adaptive character may coexist in two groups which have a similar mode of life, without indicating any affinity between them, because it mily have been acquired by each independently, to enable it to fill a similar place in nature. In such cases it is found to be an almost isolated character, apparently connecting two groups which otherwise differ radically. Non-adaptive, or purely structural characters, on the other hand, are such as have probably been transmitted from a remote ancestor; and thus indicate fundamental peculiarities of growth and development. The changes of structure renlerel necessary by modifications of the habits or instincts of the different species, have been made, to a great extent, independently of such characters ; and as several of these may always be found in the same animal their value becomes cumulative. We thus arrive at the sceming para lox, that the less of direct use is apparent in any peculiarity of structure, the greater is its value in indicating truc, though perhaps remote, affinities; while any peculiarity of an organ which seems essential to its possessor's well-being is often of very little value in indicating its affinity for other creatures.

This somewhat technical discussion will, it is hoped, enable the general reader to understand some of the more important principles of the modern or natural classification of animals, as distinguished from the artificial system which long prevailed. It will also afford him an easily remembered example of those principles, in the radical distinctness of two families of birds often confounded together,—the sun-birds of the Eastern Hemisphere, and the humming-birds of America; and in the interesting fact that the latter are essentially swifts—profoundly modified, it is true, for an aürial and flower-haunting existence, but still bearing in many important peculiarities of structure the unmistakable evidences of a common origin.

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V.

THE COLOURS OF ANIMALS AND SEXUAL

SELECTION.

General Phenomena of Colour in the Organic World – Theory of leit anı

Light as producing Colour-Chanyes of Colour in Animals produced by Coloured Light-Classification of Organic Colours --Protective Colours - Warning Colours-Sexual Colours-- Typical Colours - The Nature of Colour-Colour a normal product of Organization-Theory of Protective Colours-Theory of Warning Colours-Theory of Sexual Colours--Colour

means of Recognition-Colour proportionate to Integumentary Development -Selection by l'emales not a cause of Colour--Probable use of the Horns of Beetle :-Cause of the greater brilliance of some Female Insects-Theory of display of Ornaments by Males - Natural Selection as neutralizing Sexual Selection-- Theory of Typical Colours-Colourdevelopment as illustratel by Ilumming-birds-- Local causes of Colourdevelopment -Summary on Colour-developinent in Animals.

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There is probably no one quality of natural objects from which we derive so much pure and intellectual enjoyment as from their colours. The heavenly blue of the firmament, the glowing tints of sunset, the exquisite purity of the snowy mountains, and the endless shades of green presented by the verdurc-clad surface of the carth, are a never-failing source of pleasure to all who enjoy the inestimable gift of sight. Yet these constitute, as it were, but the frame and background of a marvellous and ever-changing picture. In contrast with these broad and soothing tints, we have presented to us in the vegetable and animal worlds, an infinite variety of olijects adorned with the most beauti

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