Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

EQUATORIAL

Online Encyclopedia
Originally appearing in Volume V14, Page 270 of the 1911 Encyclopedia Britannica.
» Make a correction to this article.
» Add information or comments to this article.
Spread the word: del.icio.us del.icio.us it!

EQUATORIAL See also:

ZoNE.—Roughly speaking, the See also:borders of this zoological zone coincide with the See also:geographical limits of the tropics of See also:Cancer and Capricorn; its characteristic forms, however, extend in undulating lines several degrees both See also:north-wards and southwards. Commencing from the See also:west See also:coast of See also:Africa, the See also:desert of the See also:Sahara forms a boundary between the equatorial and See also:northern zones; as the boundary approaches the See also:Nile, it makes a sudden sweep towards the north as far as northern See also:Syria, crosses through See also:Persia and See also:Afghanistan to the See also:southern ranges of the Himalayas, and follows the course of the Yang-tse-Kiang, which receives its contingent of equatorial fishes through its southern tributaries. Its continuation through the North Pacific may be indicated by the tropic, which strikes the coast of See also:Mexico at the southern end of the Gulf of See also:California. Equatorial types of See also:South See also:America are known to extend so far northwards; and, by following the same See also:line, the West See also:India Islands are naturally included in this zone. Towards the south the equatorial zone embraces the whole of Africa and See also:Madagascar, and seems to extend still farther south in See also:Australia, its boundary probably following the southern coast of that See also:continent; the detailed See also:distribution of the fresh-See also:water fishes of south-western Australia has been little studied, but the tropical fishes of that region follow the See also:principal water-course, the See also:Murray See also:river, far towards the south and probably to its mouth. The boundary-line then stretches to the north of See also:Tasmania and New See also:Zealand, coinciding with the tropic until it strikes the western slope of the See also:Andes, on the South See also:American continent, where it again bends southward to embrace the See also:system of the Rio de la See also:Plata. The four regions into which the equatorial zone is divided arrange themselves into two well-marked divisions, one of which is characterized by the presence of Cyprinid fishes, combined with the development of Labyrinthic Percesoces (Anabantidae and Ophiocephalidae) and Mastacembelids, whilst in the other these types are absent. The boundary between the, Cyprinoid and Acyprinoid See also:division seems to follow the now exploded See also:Wallace's line—a line See also:drawn from the south of the Philippines between See also:Borneo and See also:Celebes, and farther south between See also:Bali and See also:Lombok. Borneo abounds in Cyprinids; from the Philippine Islands a few only are known, and in Bali two See also:species have been found; but none are known from Celebes or Lombok, or from islands situated farther See also:east. The See also:Indian region comprises See also:Asia south of the Himalayas and the Yang-tse-Kiang, and includes the islands to the west of Celebes and Lombok. Towards the north-east the See also:island of See also:Formosa, which also by other parts of its See also:fauna shows the characters of the equatorial zone, has received some characteristic See also:Japanese See also:freshwater fishes. Within the geographical boundaries of See also:China the freshwater fishes of the tropics pass gradually into those of the northern zone, both being separated by a broad, debateable ground.

The affiuents of the See also:

great river traversing this See also:district are more numerous from the south than from the north, and carry the southern fishes far into the temperate zone. Scarcely better defined is the boundary of this region towards the north-west, in which fishes were very poorly re-presented by types See also:common to India and Africa. The See also:African region comprises the whole of Africa south of the Sahara. It might have been conjectured that the more temperate See also:climate of its southern extremity would have been accompanied by a conspicuous difference in the See also:fish fauna. But this is not the See also:case; the difference between the tropical and southern parts of Africa consists simply in the See also:gradual disappearance of specifically tropical forms, whilst Silurids, Cyprinids and even Anabas penetrate to its southern coast; no new See also:form, except a Galaxias at the Cape of See also:Good See also:Hope, has entered to impart to South Africa a See also:character distinct from the central portion of the continent. In the north-east the African fauna passes the See also:isthmus of See also:Suez and penetrates into Syria; the system of the See also:Jordan presents so many African types that it has to be included in a description of the African region as well as of the Europaeo-See also:Asiatic. The boundaries of the Neotropical or Tropical American region have been sufficiently indicated in the See also:definition of the equatorial zone. A broad and most irregular See also:band of See also:country, in which the South and North American forms are mixed, exists in the north. The Tropical Pacific region includes all the islands east of Wallace's line, New See also:Guinea, Australia (with the exception of its south-eastern portion), and all the islands of the tropical Pacific to the See also:Sandwich See also:group.

End of Article: EQUATORIAL

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.
Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
EQUATOR (Late Lat. aequator, from aequare, to make ... 		[next]
EQUATORIAL SYSTEM

Site © 2006 - Net Industries