PEIMATBS FEOM MADAGASCAE. 143 



In endeavouriug to answer these questions there are certain considerations which 

 might be expected a ■priori to offer some guidance as to the directions in which a 

 solution of these problems might be looked for. 



We might begin by asking the question ; What would be the probable course of 

 evolution of a group of Primates isolated since early or middle Tertiary times, confined 

 to a limited area, and removed from competition with the dominant Mammalian groups 

 which at a later date spread over the African Continent \ 



Various analogies suggest a probable answer to such a question. The Malagasy 

 flora (in which, according to Baron, three-fourths of the species and one-sixth of the 

 genera are peculiar to the island) would lead us to expect a considerable amount of 

 specialisation and divergence from the most nearly allied continental forms. Again, 

 even a cursory view of the Malagasy representatives of certain other Mammalian 

 orders — e. g. the Insectivora and Rodentia — not to mention the non-Mammalian 

 groups — would fully confirm this surmise. 



Now it is evident that the course of evolution which has pre-eminently characterised 

 the Primates on the great land-areas has been one of brain-development. We shall, 

 indeed, probably be justified in maintaining that it has been by the acquisition 

 of superior brain-power rather than by superior strength that the members of the 

 order as a whole have been able to escape extinction. 



The removal of a group of Primates from connexion with extensive continental 

 areas, and their isolation in a large island, would probably in course of time so modify 

 the conditions of existence as to eliminate much of the struggle which had hitherto 

 been one of the main factors of the brain-development of the race. One might 

 therefore expect an arrest of such development, and possibly even a " retrogressive 

 evolution " leading to actual degeneracy and loss of brain-substance. 



Now the evidence brought to light by recent discoveries does in fact substantiate 

 these a priori surmises. 



In the existing Lemurs of Madagascar we have a highly specialised group many of 

 which have widely diverged from their nearest representatives in other parts of the 

 world. Chiromys may be taken as an extreme instance of this specialisation. 



In the case of the Indrisinae we have been able definitely to connect the existing 

 genera with various extinct subfossil forms which in many of their characters give 

 striking evidence of descent from Ape-like ancestors. 



These pithecoid subfossil Lemuroids themselves, however, show signs of specialisation 

 and retrogressive changes, in some cases carried even further than in the extant 

 genera. 



Now in order to bring into clearest relief the fact that these Malagasy genera living 

 and extinct of the Indrisine group do, considered as a whole, retain many charac- 

 teristics which undoubtedly point to descent from Ape-like ancestors already possessing 

 most of the features which we associate with the true Monkeys, I propose to discuss 



