4,4 REPORT—1905. 
joined to Africa; and as the Cichlids of Madagascar are essentially African in 
character, two out of the three genera being identical, we are justified in 
believing that the Cichlids already existed in Africa at some time between the 
Middle Eocene and the Lower Miocene. But then what about the Indian and 
Ceylonese species of the genus Etroplus, which are not so closely allied to Paretroplus 
of Madagascar as was formerly believed? The land-area which once connected 
Madagascar direct with India had ceased to exist in Lower Tertiary times, and 
we must therefore assume that the Cichlids reached India from Africa through 
South-Western Asia, which is quite possible, or else that they are immigrants from 
the North. The latter supposition would harmonise with what I believe may have 
been the original mode of dispersion of this family on the assumption that the 
North American Middle Eocene Priscacara really represent the ancestral stock 
of the Cichlids. These fishes would have ranged over North America and 
Northern and Eastern Asia, which were then one continent. That we have no 
paleontological evidence of this distribution there is no wonder, since we know 
nothing of Eocene fresh-water fishes on the Asiatic continent; and when, later, 
India and Africa became connected with the Asiatic-American continent, they 
migrated southwards and westwards, and for climatic and other reasons at once 
flourished in and spread all over Africa, and especially in the newly formed Lake 
Tanganyika. 
This third hypothesis has this advantage over the two others, that it does 
not postulate any land-areas in late Eocene or Miocene times, for which there 
is at present no sufficient evidence, nor a pre-Tertiary and marine origin for 
the family Cichlidee, which is wholly improbable and receives no support from 
paleontology. 
On the other hand, it is undeniable that the hypothesis of a South Atlantic 
land communication in the Eocene has much in its favour, and when this is 
really established all difficulty in explaining the distribution of the Cichlids 
will have disappeared. In the meanwhile, to use an appropriate metaphor, we 
must not construct bridges without being sure of our points of attachment, 
otherwise they are liable to collapse as geological knowledge progresses, 
Toe MasracemBrLipm.—In dealing with the distribution of fresh-water 
fishes in his ‘ Introduction to the Study of Fishes,’ Dr. Giinther has observed that, 
‘as a general rule a genus or family of fresh-water fishes is regularly dispersed 
and most developed within a certain district, the species and individuals becoming 
scarcer towards the periphery as the type recedes more from its central home, 
some outposts being frequently pushed far beyond the outskirts of the area 
occupied by it.” I do not think there is much to say in favour of this principle, 
which is often opposed to well-established facts in geological history; and 
it is interesting in this connection to observe how in the case of the 
Mastacembelide, a highly specialised family akin to the Acanthopterygians, and 
possibly derived from the Blenniide, recent discoveries have reversed the state 
of things that appeared at the time Dr. Giinther drew up his conclusions. 
‘ Mastacembelus and Ophiocephalus, genera characteristic of the Indian region,’ 
he says, ‘emerge seyerally by a single species in West and Central Africa’; and, 
further, when comparing the fishes of the Indian and African regions, he adds: 
‘A few species only have found their way into Africa.” At present we are 
acquainted with thirty-eight species of Mastacembelus: fourteen from the Indo- 
Malay region, one from Syria and Mesopotamia, and twenty-three from Tropical 
Africa. The distribution of these fishes, the fossil remains of which are still 
unknown, has probably once been a continuous one, climatic and hydrographic 
conditions possibly accounting for the present discontinuity. We have no data 
from which to decide whether the Mastacembelids first appeared in Asia or in 
Africa, or simultaneously in both parts of the world, as is quite possible on the 
assumption that the family originated in the Eocene sea extending from the 
Western Soudan to India. 
This concludes our review of the affinities and past history of the principal 
fresh-water types which characterise the present African fish-fauna. We have 
