August 2^, 1905] 



NA TURE 



419 



Alps and South-Western Asia. With two exceptions, all 

 the Cyprinids are confined to the northern watershed of 

 the Atlas, in which varieties of our River Trout and our 

 Stickleback also occur; but Barbus callensis and the 

 Phoxinellus occur also in the Algerian and Tunisian 

 Sahara, showing that, as in other groups of animals, no 

 sharp delimitation can be drawn between the Palaearctic 

 and .Ethiopian regions of Barbary. 



Of three Cyprinodonts one, from the high plateaux, 

 inhabits also Spain ; another, more generally distributed, 

 is known from Sicily, Syria, and North-East Africa ; whilst 

 the third, remarkable for the absence of ventral fins, is 

 monotypic of a genus named Tellia — a misnomer, as it is 

 not found in the Tell, but on the high plateaux of Algeria, 

 at altitudes of from 2000 to 3000 feet, not Sooo, as stated 

 by Danbeck. 



Three Cichlids are known from the Northern Sahara, 

 one, a Tilapia, being restricted to Eastern Algeria and 

 Tunisia, whilst the two others, a Hcmichromis and a 

 Tilapia, extend lo Lower Egypt, and are besides widely 

 distributed in Tropical Africa. The Cichlids, along with 

 the Cyprinodon, the Barbus, and the Phoxinellus mentioned 

 above, are often ejected by artesian wells, and the fact 

 has given rise to much discussion. The latest investigator 

 of this phenomenon, the distinguished engineer, M. George 

 Rolland, confirms the opinion, expressed by the late Sir 

 Lambert Playfair and M. Letourneux in 1871, that these 

 fishes normally live and breed in the lakes and wells ex- 

 posed to air and ITght, and that their presence in the 

 underground sheets of water with which the lakes com- 

 municate is merely an episode, and as it were an incident 

 in the voyages which they undertake from one opening 

 to the other. There is therefore no justification for the 

 term " realm of the Trogloichthydae " which has been pro- 

 posed by Dambeck for North-West Africa. 



The other fishes which complete the list are of direct 

 marine derivation, as the anadromous Shad and the cala- 

 dromous Eel and Grey Mullets, or such as have recently 

 adapted themselves to permanent existence in fresh water, 

 like the Syngnathus discovered by Sir L. Playfair, the 

 Atherina, which occurs also in various fresh-water or 

 brackish lakes in Southern Europe and Egypt and in the 

 Caspian Sea, two Gobies and a Blenny, the latter being 

 also known from fresh waters in the South of France and 

 in Italy. The occurrence of an otherwise strictly marine 

 species of Blenniids (Crisliceps argentatits) in the fountain 

 of Ain Malakoff, in the high plateaux of Algeria, rests on 

 the testimony of a naturalist of Algiers and needs con- 

 firmation. 



n. The MEGAroTAMiAN Sub-region. 

 The Nile, tlie Niger, the Gambia and the Senegal, the 

 Congo, and the Zambesi, with their numerous iMormyrids, 

 Characinids, Silurids, and Cichlids, have much the same 

 general character, which points to many of the generic 

 types having radiated from a common centre of origin, no 

 doubt in those great central lakes which are believed to 

 have existed in Middle Tertiary times. Lake Chad, the 

 ichthyic fauna of which was until quite recently unknown, 

 represents the dwindling remains of a larger basin which 

 communicated until comparatively recent times with both 

 the eastern and western river-systems, thus accounting for 

 the great resemblance between the fishes of the Nile and 

 those of the rivers of the Atlantic watershed north of the 

 Cameroons, 46 species out of loi known from the Nile 

 (without the great lakes by which it is now fed) being also 

 found in the Niger, the Senegal, or the Gambia, or in all 

 three, and most of these have been recently found in Lake 

 Chad and the rivers emptying into it. The collection made 

 in Lake Chad by Captain Gosling, and sent by him to 

 the British Museum, contains representatives of twenty- 

 four species, all of which were previously known from 

 both the Nile and the Niger, thus strikingly confirming 

 conclusions arrived at from a study of the fauna of those 

 two river-systems. Collections sent to the Paris Museum 

 by the Chevalier and Decorse Mission, and worked out by 

 Dr. Pellegrin, add twenty-five species to the above number, 

 two described as new, two Nilotic, eight West African, 

 five Congolese, the rest being common to the eastern and 

 western river-systems. The Congo differs more consider- 

 ably, and must therefore have been separated from the 



NO. 1869, VOL. 72] 



Nile-Chad-Niger for a longer period, only 15 out of its 

 265 species (excluding the Tanganyika) occurring also in 

 the Nile, and eleven in the Chad. When we reach the 

 district of the sources of the Congo, the so-called Katanga 

 district, we find a mi.xture of Congo and Zambesi forms, 

 which points tp a former reversal of the drainage of parts 

 of the elevated dividing range. Lake Mwero belongs to 

 this district ; although so near to Lake Tanganyika, it 

 has no fish in common with it except a few of very wide 

 distribution. Lake Bangweolo, also in the same district, 

 is said to swarm with fishes, Silurids and Cichlids 

 especially, but they have never been collected. The 

 Zambesi, so far as it has been explored at present, is the 

 poorest in fishes of the great rivers, and it differs from the 

 others in one important point — the absence of the Poly- 

 pterida;. The great lakes differ considerably in their fishes 

 from the river-systems into which they drain. 



As pointed out eleven years ago by Prof. Gregory, the 

 system of the head waters of the Nile must have been very 

 differently arranged in times geologically quite recent. 

 This is proved by what we know of the great lalces north 

 of Tanganyika. Thus, of the species known from Lake 

 Victoria, barely one-fourth occur also in the Nile, the rest 

 being mostly endemic ; whilst Lake Rudolf, which has now 

 no communication with the Nile, has four-fifths of its 

 species in common with that system. Lakes Albert and 

 Albert Edward are very insufficiently explored and have 

 only yielded a few species, one-half of which are Nilotic. 

 Two fishes, Cyprinids, are all we know from Lake Baringo, 

 one being a widely distributed Nile species, the other an 

 East African. We must conclude from these data that 

 Lake Victoria has long been isolated, whilst Lake Rudolf 

 has until very recently been in communication with the 

 Nile. 



Lake Tsana, which is now the source of the Blue Nile, 

 has recently yielded a large collection of fishes, showing 

 a great variety of Cyprinids, either endemic or identical 

 with species occurring in the eastern watershed, and closely 

 allied to those of Palestine, but with no special Nile 

 affinities. The discovery of a Loach (Nemachilus), the first 

 known from Africa, points to an immigration from the 

 Jordan, probably through the old Erythrean Valley. The 

 only species which Lake Tsana has in common with the 

 Nile (Tilapia nilotica) occurs also in the Hawash and in 

 the Jordan. 



From the vastly increased information we now possess 

 of the fishes of the Nile-system, we are justified in believing 

 in great changes in the hydrography of this part of Atrica. 

 Ihe fishes of Lake Tsana would support Prof. Gregory's 

 conclusion as to a communication with the Jordan through 

 a river running along what is now the Red Sea, whilst 

 those of the Lower Nile point to a direct communication 

 between the latter and the Jordan, as advocated by Prof. 

 Hull, migrations along two distinct channels having taken 

 place at a time when the Mediterranean did not extend 

 so far to the east as it does at present, and the Indian 

 Ocean had not penetrated into the Erythrean Valley. A 

 better knowledge of the fishes of Egypt has disposed of 

 Prof. Gregory's arguments against a former communication 

 between the Lower Nile and the Jordan. 



The Nile in its widest sense, but without the great lakes, 

 has loi species, not including those that enter the sea : 

 twenty-seven do not extend north of Khartoum, whilst only 

 six are restricted to the river below the First Cataract. 

 The most important additions made since Dr. Giinther's 

 account of them in " Petherick's Travels " are several 

 Mormyrs, Barbus, and Synodontis, three Cichlids, a Xeno- 

 mystus, a Nannaethiops, a Discognathus, a Barilius, a 

 Chiloglanis, a Fundulus, an Eleotris, and the remarkable 

 genera Physailia, Andersonia, and Cromeria, the latter the 

 type of a new family. 



ThanUi to the collections made by Sir Harry Johnston 

 and Col. Dclni^ Radcliffe, with the help of Mr. Doggett, 

 and by M. Alluaud, supplementing those of Dr. Fischer, 

 we may now draw up a list of twenty-five species from 

 Lake Victoria. The comparative scarcity of animal and 

 vegetable life in this great lake perhaps precludes expect- 

 ation of a great increase in the number of species in the 

 course of further exploration. Most of the species are 

 endemic, and among the most remarkable types mav be 

 mentioned a Discognathus, a Mastacembelus (probably the 



