2 PERCY SLADEN TRUST EXPEDITION 



may be considered as thoroughly representative of its Lepidopterous fauna, though from 

 their general fades I should judge there is yet more of great interest to be obtained 

 from the small patches of primitive jungle that still remain — especially on Silhouette. 

 It is of course impossible, even for a collector of the greatest ability, to exhaustively work 

 any single order of insects in a locality when engaged in making collections covering all 

 orders. The deductions of importance, which can be made from such collections as I 

 am about to describe, relate in the main to questions of geographical distribution ; in 

 the present paper we have two entirely distinct problems to consider: (l) that of the 

 Seychelles Archipelago ; (2) that of Aldabra and the neighbouring islands. 



(1) The Seychelles, with the exception of Bird and Dennis Islands, consist of 

 granitic rocks, with a maximum elevation of 3000 ft. The islands were formerly clothed 

 with a jungle of plants very largely peculiar to the archipelago, though cultivation has 

 now reduced it to small areas left on the higher peaks. Professor Stanley Gardiner, 

 both for geographical and biological reasons, considers that the Seychelles form the last 

 remaining portion of a land-bridge which connected India and Madagascar between 

 carboniferous and tertiary times, while he also considers that formerly the whole 

 Seychelles bank (2000 square miles) was capped with land which has been cut down 

 by sea abrasion to the few small islands which at present exist : the lepidopterous fauna, 

 therefore, must be considered in connection with this view. 



(2) The atoll of Aldabra and also the neighbouring islands are shown by their 

 structure to have risen from the sea and to have never been connected with any other 

 land : the entire insect fauna, therefore, must have arrived by sea, being in the main 

 derived from forms driven by wind from the neighbouring lands. Aldabra is quite 

 uncultivated, and much of it had not been explored before my visit, and therefore 

 transference by human agency can be almost neglected. It is covei^ed with a vegetation 

 derived entirely from Madagascar — a most important fact, as insects arriving from that 

 region will find in many cases their original food plant. 



Considering the Seychelles problem first, a glance at a map of the Indian Ocean 

 will show that to the east and north of the archipelago is a chain of coral islands partly 

 bridging the gap between it and India : this bridge must have been of great assistance 

 in the distribution of those Indian and widely occurring forms, which can exist on the 

 limited number of food plants provided by a coral island. To the south-west are the 

 coral islands of the Amirantes, but there are no other " stepping stones " between the 

 Seychelles and Africa. To the south as far as Aldabra are a few small coral rocks, but 

 these are not of a nature to assist largely in the distribution of continental forms. 



The winds in the Seychelles region consist of the S.E. Trades from May to 

 September and of the N.W. Monsoon, usually light north-westerly breezes, with 

 occasional squalls, from October to April. Of these two winds the latter are probably 

 the most useful in distribution, as the S.E. Trades, though stronger, cross a large tract 

 of open sea. 



Currents cannot be of very great assistance to the larger forms which we are 

 considering, though they may have distributed wood-feeding Tortricids and Tineids 

 {vide E. Meyrick on the Tortricina and Tineina of the expedition). The Seychelles 



