Annals of the Transvaal Museum. 
35 
genus Rana and the various genera which are minus the supernumerary 
phalanges. But to return to the other section, this is strongly developed 
in Madagascar, and although three out of the four genera occur elsewhere, 
the whole section is no doubt truly endemic there, as indicated by the 
large peculiar genus Mantidactylus and the marked development of the 
genus Rhacophorus. Two of the genera Rappia and Megalixalus are 
common to South Africa and Madagascar, whilst the genus Rhacophorus 
has many species both in Madagascar and the Indian region, but these 
facts do not necessarily imply a specially great antiquity for such genera, 
as, being of arboreal habit, like the great majority of the members of the 
same section, they would no doubt be able to effect their continuous dis- 
persal during the greater part of the time when the direct land connections 
were dissolving and under conditions which would altogether isolate 
terrestrial or purely aquatic frogs which unanimously abhor salt water. 
Somewhat parallel instances amongst mammals are known, and Dr. 
Standing explains the occurrence in Madagascar of such late forms as pigs 
and hippopotami, and the absence of other groups which are known to 
have existed on the African continent at an earlier date, on the hypothesis 
that Madagascar and Africa have remained in connection up to a very late 
tertiary date by means of a low-lying isthmus covered with dense jungle 
and intersected by swampy tracts : this would offer but little obstacle to 
wild pig, but would be a complete barrier to almost all other mammals 
except purely arboreal forms. 
As Dr. Gadow has pointed out, the entire sub-family of Raninae is 
in its fulness and diversity of development essentially palaeo tropical ; 
from which we may infer that its centre of origin was the great Indo-Oceanic 
continent, and I believe that the arboreal section of Madagascar and 
South Africa represents the original stock without much modification — 
but this is a point for anatomical investigation. As already mentioned, 
the African members of the other section, the genus Rana excepted, are 
all peculiar to the region so that they were probably developed in this 
continent: several of them have near allies in eastern Asia, e.g. 
Phrynobatrachus and Arthroleptis appear to be closely related to Oreo- 
batrachus from Mount Kina Balu in Borneo, whilst Cornufer of Austro-Malaya 
and Polynesia has a very near ally in Petropedetes of the Cameroons and 
Gabun. The land connections which are implied in these relationships 
were presumably in existence subsequent to the isolation of the main island 
of Madagascar. It should be added also that there are a few Ranid genera 
in tropical South America and Central America : this assembly seems 
to be a natural one, but its relationships are unknown to me. I judge 
from the distribution that they come from the old world by way of the 
transatlantic bridge. 
As regards the genus Rana, its distribution suggests an old-world 
origin, and in the new world it appears likely that it travelled from the 
North to South America : if we suppose that it had its origin in Africa, 
it must be understood that this could only have happened subsequent to 
the dissolution of the transatlantic land bridge. 
Probably the most distinctive section of this large and widely dispersed 
genus is that which was formerly included under the generic name 
