Page images

fernandensis, one of the Tyrannidæ ; and two humming-birds, Eustephanus fernandensis and E. galeritus. The first is a widespread South Temperate species, the two next are peculiar to the island, while the last is a Chilian species which ranges south to Tierra del Fuego. But ninety miles beyond this island lies another, called “Mas-a-fuero," very much smaller ; yet this, too, contains four species of similar birds; one, Oxyurus mas-a-fuero, allied to the wide-spread South Temperate O. spinicauda, and Cinclodes fusus, a South Temperate speciesboth Dendrocolaptidæ ; with a humming-bird, Eustephanus leyboldi, allied to the species in the larger island. The preceding facts are taken from papers by Mr. Sclater in the Ibis for 1871, and a later one in the same journal by Mr. Salvin (1875). The former author has some interesting remarks on the three species of humming-birds of the genus Eustephanus, above referred to. The Chilian species, E. galeritus, is green in both sexes. E. fernandensis has the male of a fine red colour and the female green, though differently marked from the female of E. galeritus. E. leyboldi (of Mas-a-fuera) has the male also red and the female green, but the female is more like that of E. galeritus, than it is like the female of its nearer ally in Juan Fernandez. Mr. Sclater supposes, that the ancient parent form of these three birds had the sexes alike, as in the present Chilian bird ; that a pair (or a female having fertilised ova) reached Juan Fernandez and colonised it. Under the action of sexual selection (unchecked by some conditions which had impaired its efficacy on the continent) the male gradually assumed a brilliant plumage, and the female also slightly changed its markings. Before this change was completed the bird had established an isolated colony on Mas-a-fuera ; and here the process of change was continued in the male, but from some unknown cause checked in the female, which thus remains nearer the parent form. Lastly the slightly modified Chilian bird again reached Juan Fernandez and exists there side by side with its strangely altered cousin.

All the phenomena can thus be accounted for by known laws, on the theory of very rare accidental immigrations from the

mainland. The species are here so very few, that the greatest advocate for continental extensions would hardly call such vast causes into action, to account for the presence of these three birds on so small and so remote an island, especially as the union must have continued down to the time of existing species. But if accidental immigration has sufficed here, it will also assuredly have sufficed where the islands are larger, and the chances of reaching them proportionately greater; and it is because an important principle is here illustrated on so small a scale, and in so simple a manner as to be almost undeniable, that we have devoted a paragraph to its elucidation. A few Coleoptera from Juan Fernandez present analogous phenomena. All belong to Chilian genera, while a portion of them constitute peculiar species. Land-shells are rather plentiful, there being about twenty species belonging to seven genera, all found in the adjacent parts of South America; but all the species are peculiar, as well as four others found on the island of Mas-a-fuera.

III. Tropical North America, or the Mexican Sub-region.

This sub-region is of comparatively small extent, consisting of the irregular neck of land, about 1,800 miles long, which connects the North and South American continents. Almost the whole of its area is mountainous, being in fact a continuation of the great range of the Rocky Mountains. In Mexico it forms an extensive table-land, from 6,000 to 9,000 feet above the sea, with numerous volcanic peaks from 12,000 to 18,000 feet high; but in Yucatan and Honduras, the country is less elevated, though still mountainous. On the shores of the Caribbean Sea and Gulf of Mexico, there is a margin of low land from 50 to 100 miles wide, beyond which the mountains rise abruptly; but on the Pacific side this is almost entirely wanting, the mountains rising almost immediately from the sea shore. With the exception of the elevated plateaus of Mexico and Guatemala, and the extremity of the peninsula of Yucatan, the whole of Central America is clothed with forests; and as its surface is much broken up into hill and valley, and the volcanic soil of a large portion of it is very fertile, it is altogether well adapted to support a varied fauna, as it does a most luxuriant vegetation. Although many peculiar Neotropical types are absent, it yet possesses an ample supply of generic and specific forms; and, as far as concerns birds and insects, is not perhaps inferior to the richest portions of South America in the number of species to be found in equal areas. Owing to the fact that the former Republic of Mexico comprised much territory that belongs to the Nearctic region, and that many Nearctic groups extend along the high-lands to the capital city of Mexico itself, and even considerably further south, there is much difficulty in determining what animals really belong to this sub-region. On the low-lands, tropical forms predominate as far as 28° N. latitude; while on the cordilleras, temperate forms prevail down to 20°, and are found even much farther within the tropics. Mammalia.-Very few 'peculiar forms of Mammalia are restricted to tropical North America; which is not to be wondered at when we consider the small extent of the country, and the facility of communication with adjacent sub-regions. A peculiar form of tapir (Elasmognathus bairdi) inhabits Central America, from Panama to Guatemala, and, with Myzomys, a genus of Muridae, are all at present discovered. Bassaris, a remarkable form of Procyonidae, has been included in the Nearctic region, but it extends to the high-lands of Guatemala. Heteromys, a peculiar genus of Saccomyidae or pouched rats, inhabits Mexico, Honduras, Costa Rica, and Trinidad. Five genera of monkeys extend here, Ateles, Mycetes, Cebus, Nyctipithecus, and Saimiris; the two former alone reaching Mexico, the last only going as far as Costa Rica. Other typical Neotropical forms are Galera, the tayra, belonging to the weasel family; Nasua, the coatimundi; Dicotyles, the peccary; Cercolabes, the tree porcupine; Dasyprocta, the agouti; Caelogenys, the paca; Cholapus, and Arctopithecus, sloths; Cyclothurus, an ant-eater; Tatusia, an armadillo; and Didelphys, oppossum. Of Northern forms. Sorew, Vulpes, Lepus, and Pteromys reach Guatemala. Birds—The productiveness of this district in bird life, may be estimated from the fact, that Messrs. Salvin and Sclater have catalogued more than 600 species from the comparatively small territory of Guatemala, or the portion of Central America between Mexico and Honduras. The great mass of the birds of this sub-region are of Neotropical families and genera, but these are intermingled with a number of migrants from temperate North America, which pass the winter here; with some northern forms on the high-lands; and with a considerable number of peculiar genera, mostly of Neotropical affinities. The genera of birds peculiar to this sub-region belong to the following families:–Turdidae (2 genera); Troglodytidae (1 gen.); Vireonidae (1 gen); Corvidae (2 gen); Ampelidae (1 gen); Tanagridae (1 gen.); Fringillidae (2 gen); Icteridae (1 gen); Formicariidae (2 gen); Tyrannidae (2 gen); Cotingidae (1 gen.); Momotidae (1 gen); Trogonidae (1 gen.); Trochilidae (14 gen.); Conuridae (1 gen); Cracidae (2 gen); Strigidae (1 gen); in all 37 genera of land-birds. The Neotropical families that do not extend into this sub-region are, Pteroptochidae; the sub-family Furnariinae of the Dendrocolaptidae; the sub-family Conophaginae of the Tyrannidae; the sub-family Rupicolinae of the Cotingidae; Phytotomidae; Todidae; Opisthocomidae; Chionididae; Thinocoridae; Cariamidae; Psophiidae; Eurypygidae; Palamedeidae; and Struthionidae. On the other hand Paridae, Certhiidae, Ampelidae, and Phasianidae, are northern families represented here, but which do not reach South America; and there are also several northern genera and species, of Turdidae, Troglodytidae, Mniotiltidae, Vireonidae, Fringillidae, Corvidae, Tetraonidae, and Strigidae, which are similarly restricted. Some of the most remarkable of the Neotropical genera only extend as far as Costa Rica and Veragua, countries which possess a rich and remarkable fauna. Here only are found an umbrella bird, (Cephalopterus glabricollis); a bell bird (Chasmorhynchus tricarunculatus); and species of Dacnis (Ceroebidae), Buthraupis, Eucometis, Tachyphonus (Tanagridae), Xiphorhynchus (Dendrocolaptidae); Hypocnemis (Formicariidae); Euscarthmus (Tyrannidae); Attila (Cotingidae); Piprites (Pipridae); Capito, Tetragonops (Megalaemidae); Selenidera (Rhamphastidae); Neomorphus Cuculidae); Monasa (Bucconidae); many genera of Trochilidae; and Nothocercus (Tinamidae); none of which extend further north. A considerable number of the peculiar genera noted above, are also found in this restricted area, which is probably one of the richest ornithological districts on the globe. Reptiles.—These are much less known than the preceding classes, but they afford several peculiar and interesting forms. Snakes are perhaps the least remarkable; yet there are recorded 4 peculiar genera of Calamariidae, 1 of Golubridae, 1 of Homalopsidae, 3 of Dipsadidae; while Boa and Elaps are in common with South America. Lizards are much more specially developed. Chirotes, one of the Amphisbaenians, is confined to Mexico and the southern part of the Nearctic region; Heloderma forming a peculiar family, Helodermidae, is Mexican only; Abronia and Barissia (Zonuridae) are also Mexican, as is Siderolampus belonging to the Scincidae, while Blepharactitis (same family) inhabits Nicaragua; Brachydactylus, one of the geckoes, is from Costa Rica; while Phymatolepis, Lamanctus, Corytheolus, Cachriw, Corythophanes and Chamaeleopsis, all belonging to the Iguanidae, are confined to various parts of the sub-region. In the same family we have also the Antillean, Cyclura,and the Nearctic Phrynosoma and Tropidolepis, as well as the wide-spread American genus Anolius. Among the tortoises, Staurotypus, allied to Chelyara, is found in Mexico and Guatemala; and another genus, Claudius, has been lately described from Mexico. Amphibia.-These are chiefly Batrachians; Rhinophryna (forming a peculiar family) being confined to Mexico; Triprion, a genus of Hylidae, inhabiting Yucatan, with Leyla and Strabomantis (Polypedatidae) found only in Costa Rica and Veragua, are peculiar genera. The Salamandridae, so abundant in the Nearctic region, are represented by a few species of Amblystoma and Spelerpes. Fresh-water fish—Since the British Museum catalogue was published, a valuable paper by Dr. Günther, in the Transactions of the Zoological Society for 1868, furnishes much additional information on the fishes of Central America. In that part of the region south of Mexico, 106 species of fresh-water fishes are

« EelmineJätka »