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Show 1866.] PROF. W . LILLJEBORG O N THE CLASS OF BIRDS. 7 ^ Irritability seems to us to be the most distinguishing character for birds; and this should consequently be taken into consideration more than others with regard to their classification. The swimmers seem to us the lowest, from their showing a tendency to the lowest form of vertebrated animals-the fish-form. In the Aptenodytidce, where the wings resemble fins, and where they, as in all other diving birds, serve as such, we have this form most strongly designated. The heavy, clumsy structure, with small wings and short legs, also makes them generally less active than other birds, and shows a lower development of the type of bird. This, however, is not the case with all the swimmers; and the order Longipennes gives us instances where swimmers possess a high degree of activity. The Passerine birds (Passeres) seem to us to possess the highest irritability, and to be those in which the nature of birds has reached its highest development. W e do not by irritability mean the muscular strength alone, but vivacity and activity generally. Where this is most manifold, most changing and constant, it is the most developed. W e find in the Passeres " the power to stay and move with ease as well on the ground as in the trees or in the air, and to make their presence known by characteristic melodious notes" (Sundevall) ; we find them in a constant and manifold motion, and they let us constantly hear their notes either as song or as affectionate voices. The birds of prey have generally been placed highest, and been considered the most developed, in consequence of their muscular strength and strong flight, and their thereby supposed high degree of irritability ; but by keeping them in captivity we find at once that the birds of prey are dull birds, and that they, as regards irritability, are far behind the Passeres. They remain for a long time silent and quiet, and do not generally show any activity, unless they are frightened or driven by appetite for food. The Passerine birds, on the contrary, are in captivity constantly in motion, and let us incessantly hear their lively song and affectionate voices. Besides we cannot in a system place the birds of prey far from the lower groups, of the Columbine and the Gallinaceous sections, without violating natural affinities based upon important characters. They correspond with these lower groups as regards external characters in the nature of their wing-coverts, and, as regards interior anatomical characters, in the nature of their carotides communes. Some of them, for instance those of the Vulturine section, exhibit, with regard to their form, a near analogy with some of those of the two mentioned groups. We may, for instance, compare a Condor with a Turkey. A system that places the dirty Vultures highest, does not seem to us to indicate a correct idea of the nature of the birds. If we do not regard flight, which is common to almost all birds, but consider birds with regard to the various other ways of motion for which they especially are shaped, and for which their structure is also adapted, we find easily that these in general may be compre-hended in three different modes, viz.: 1st, swimming on the water ; 2nd, running on the ground ; and 3rd, climbing and jumping on |
