4i6 



NA TURE 



[August 24, 1905 



constitute the great bulk of the family both in the new 

 world and in the old, have left remains in the Oligocene 

 and later beds in North America and Europe. It is, there- 

 fore, highly probable that the Cyprinids originated as a 

 northern offshoot of the South and Central American 

 Characinids, and thence spread to Eastern Asia, at least 

 as early as the Upper Eocene. By the time (Miocene) 

 they had reached India, where they now form the great 

 majority of the fresh-water fishes, Africa had been con- 

 nected with it by a wide belt of land, and no obstacle 

 prevented their western extension. This comparatively 

 recent migration accounts for the practical identity of the 

 genera and the often very close affinity of the species of 

 the Cyprinids of India and Africa. At the same period 

 the land-area connecting India and Africa with Madagascar 

 had disappeared, and the Cyprinids never reached that 

 great island, where no doubt they would have thriven, if 

 we judge by the results of the introduction by man of the 

 gold fish, said to be in process of strongly reducing the 

 numbers of the native Malagasy fresh-water fishes with 

 which it is in a position to compete. Competition is 

 always an important factor in the distribution of a group 

 of animals, and the confinement of the Characinids to the 

 waters of the western and central parts of Africa at the 

 time of the immigration of the Cyprinids from the east 

 must be the explanation of the comparative abundance 

 of the latter and the scarcity of the former in those parts 

 of the continent east of the Rift Valley which are not 

 drained by rivers flowing from the central parts. The 

 Cvprinids must have spread more rapidly than the 

 Characinids, and being also less partial to heat they have 

 thriven in the waters of South Africa, where at present 

 only two species of Characinids — both carnivorous forms — 

 are known to extend south of the Zambesi system. Of 

 the 202 species recorded from .Africa thirteen are found 

 in North-West Africa, sixty-three in East Africa (exclusive 

 of the Zambesi), and twenty-one in South Africa. 



The Silurid.^:. — This large family is almost cosmo- 

 politan in tropical and warm regions ; and although the 

 great bulk of the species are restricted to fresh waters, 

 a certain number (chiefly of the sub-family Ariinje) occur 

 on the coasts and in the estuaries. Morphologically these 

 fishes are so closely allied to the Characinidae and 

 Cyprinidse that we must assume them to have been evolved 

 from a common ancestral stock, probably in Cretaceous 

 times ; but connecting forms such as we should expect 

 to find in deposits of that age are still unknown. The 

 Silurids appear in the Lower Eocene estuarine beds of 

 England and France, as forms closely related to the living 

 Ariinae and Bagrinse, and further allied forms follow in the 

 Middle Eocene of various parts of Europe and North 

 America. In the Upper Eocene of Lower Egypt estuarine 

 deposits contain well-preserved remains of forms which 

 appear to be only specifically separable from the Bagrus 

 still living in the Nile. The general distribution of these 

 fishes was, therefore, in early Tertiary times very much 

 the same as it is at present, and paleontology offers us 

 no clue as to where they originated. 



The exclusively fresh-water Silurids now found in Africa 

 are all generically distinct from the South American forms, 

 whilst the West African species that enter the sea belong 

 to the same genus (Arius). The two exclusively fresh- 

 water Silurids found in Madagascar show closer affinity 

 with the African than with the Indian forms, and may 

 have immigrated from Africa in the early Tertiary times 

 through the bridge which then existed, unless they have 

 been derived from marine types, which is quite possible. 



The GALAxnD.SE.— Two small fishes originally described 

 by F. de Castclnau as Loaches, and now referred to 

 Galaxias, occur on the flats near Cape Town and in the 

 Lorenz River, some twelve miles from its mouth in False 

 Bay. They are of special interest as belonging to a family 

 and genus long believed to be exclusively confined to fresh 

 waters and characteristic of the extreme south of America, 

 New Zealand, and Southern Australia. After Dr. Stein- 

 dachner had first recognised the true affinities of the Cape 

 species. Prof. Max Weber was inclined to regard this 

 interesting discovery as affording a new argument in 

 favour of the past antarctic continent on which so much 

 has been written. But Dr. Wallace was nearer the truth 

 when he suggested that a land connection within the 



NO. 1869, VOL. 72] 



period of existence of one species of fish, viz. Galaxias 

 attentiattis, known from Chili, Patagonia, Tierra del 

 Fuego, the Falkland Islands, New Zealand, and Southern 

 Australia, would have led to much more numerous and 

 important cases of similarity of natural productions than 

 we actually find, and that we must rather look to the 

 transport of the ova across the southern sea to explain 

 this very remarkable distribution. A better acquaintance 

 with the Galaxias has confirmed Dr. Wallace's supposition, 

 as it is now an established fact that some species live in 

 the sea. 



As the early Tertiary "Antarctica," as designed by 

 Prof. H. F. Osborn, does not involve South Africa, the 

 presence of species of Galaxias at the Cape cannot, even 

 on that hypothesis of continental extension, be explained 

 except on the assumption of their marine origin. 



The Knerhd^. — A monotypic family with two species, 

 one from Angola, the other from East Africa. These little 

 fishes are related to the Pikes, Esocid^e ; and there is no 

 reason that I can see against their being possibly derived 

 from them, in which case they would be of northern origin, 

 the Esocidse, now confined to the northern hemisphere, 

 being known from fresh-water deposits in Europe as far 

 back as the Oligocene. 



The Cyprinodontid.e. — The members of this large 

 family are mostly Central and .South American. They are 

 comparatively few in Africa, but have representatives in 

 every part, and also in Madagascar and the other islands 

 of the Indian Ocean. Although principally restricted to 

 fresh waters, not a few species are known to live in 

 brackish water, whilst examples are known of their occur- 

 ring far out at sea. 



The Ophiocephalid^ and Anabantid^e. — Unknown 

 fossil, and now restricted to Africa and South-Eastern 

 Asia, we have no means of telling in what part of the 

 world these two closely allied families originated. The 

 Anabantidas are more numerous in species, and these are 

 of a more generalised type, in Africa than in Asia. 



The Nandid^. — The recent discovery of Polycentropsis 

 in the Lower Niger has added a genus to a small family 

 previously known to be represented by three genera in 

 South-Eastern Asia and by two in the northern parts of 

 South America. The latter are more nearly related to the 

 African genus than the former. Too little is known of 

 the habits of these fishes to decide whether the hypothesis 

 of a migration across the Atlantic, in the days when a 

 shallow area with a string of islands connected the old 

 world and the new, answers for their distribution. Their 

 systematic position — specialised Perciformes — is against the 

 assumption of their having existed in Cretaceous or early 

 Eocene times. No fossil forms are known. 



The Osphro.menid;e. — The only African representative, 

 the genus Micracanlhus, with a single species in the 

 Ogow^, is hardly separable from the genus Betta, which, 

 with six other genera, is characteristic of the Indo-Malay 

 region and China. Paljeontology gives no information on 

 the earlier distribution of these highly specialised fishes. 

 That a type so well organised for adapting itself to all 

 sorts of waters, and so ready to acclimatise itself in any 

 part of the tropical or subtropical countries where it has 

 been transported by man, should have so restricted a range 

 seems remarkable. Were it not for the existence of this 

 African form, far away from the other members of the 

 family, one might have felt inclined to look upon the 

 Osphromenidae as a very recent group, which has not had 

 time to spread far from its original centre in South- 

 western Asia. 



The CiCHLiDiE. — As regards the number of species (179) 

 this family ranks next to the Cyprinidae (202) and the 

 Siluridfe (187) in the African fresh-water fish-fauna, and, 

 like these, it has representatives nearly all over the great 

 continent. Although Cichlids may thrive in inland waters 

 of considerable salinity, they are not known to have ever 

 been found in the sea, even near the mouths of rivers. 

 The facility with which they establish themselves in 

 isolated waters, often untenanted by other fishes, such as 

 wells in the Sahara, salt-water pools in the interior of 

 East Africa, &c., has long been known, but by what agency 

 this has been effected remains unexplained. Quite recently 

 Dr. Lonnberg has reported on the exploration of a small 



