OCR Text |
Show 1889.] CONVOLUTIONS IN BIRDS. 315 handed spiral in its second loop, whilst the fourth loop is long, and in the more piscivorous members widely open and irregularly placed. The affinity between the Coraciidce and the Alcedinidee in opposition to other groups may be expressed by the term Halcyones ; the frequent occurrence of blue non-metallic colour in these birds favours the acceptance of such a term. The Striges verge towards the plagioccelous type, but all their affinities rest with the Coraciidae and Caprimulgidae combined. These three families possess long caeca; the Alcedinidae, Cypselidae, and Trochilidae have lost them, the first of these because of their piscivorous and cancrivorous habits. The Caprimulgidce, Cypselidce, and Trochilidce agree very much with each other. They are, however, all of equivalent rank. They all have only three intestinal loops, which are short, in agreement with their principally insectivorous habits. The Trochilidae differ in the possession of a crop. The Cypselidce and Caprimulgidce are somewhat more closely related to each other, and the latter (including Podargus) turn towards the Owls. The Cypselidae are sometimes supposed to be somewhat nearly allied to the Passeres. Their alimentary system does not altogether favour such a view; but perhaps the ancestors of Colius once filled this gap, leaving their sole recent descendant now in a solitary position. The Trogonidce stand on a lower level than the Cypselidae, Trochilidae, and Coliidae, on the same level as the Caprimulgidae and Coraciidae, and connect them all with each other. How much of this is mere coincidence, I am unable to decide, owing to want of material. The Trogons still possess well-developed caeca like the Coraciidae, Caprimulgidae, and Striges, whilst all the other Coracornithes inside the isoccelous circle have lost them, or have only functionless remnants of them. W e cannot divide the whole host of Coracornithes into Meno- and Lipotyphla, because the loss of the caeca does not indicate relationship, and has been produced independently by the absence or scarcity of cellulose or chitinous substances in the food taken. The Passeres are a very uniform group, equivalent to the Halcyones, Pici, Striges, &c. Their roots lie in the anticcelous assemblage, nearer to the right than to the left in the diagram. They all possess only three loops, without indications of more; the second and third are left-handed; the second becomes a left-handed spiral, the turns of which depend upon the length of the gut; the third loop is always open, and invariably encloses the duodenum between its descending and ascending branches, the latter branch being situated on the ventral and left side of the descending branch of the duodenum. This arrangement is invariably the same, even in the Mesomyodians, and in such otherwise aberrant forms as Rupicola and Pitta. ' There is a special line which leads from the Lauiine forms through the Austrocoraces(Gymnorhina, Graucalus, Strepera, Para-diseidae, &c.) into the Coraces proper, which latter have produced some special modifications of the intestinal convolutions, and may be looked upon as the last and highest blossom of the Avian tree. |