318 PERCY SLADBN TEUST EXPEDITION. 



Macroglossuni corythus, Cephonodes pious, Hippotion velox. These may have come 

 direct from Ceylon or from the Malayo- Australian region via Cocos-Keeling. It seems 

 obvious that the Maldives have not been the means of communication, as none of these 

 species are found in that group, a fact which lends support to the idea that they have 

 come in from the south-eastward. 



(5) Species peculiar to the Australian region -.—Junonia vellida. This butterfly 

 seems to be a native of Australia, whence it has spread into the southern part of the 

 Malayan region. There is at least no doubt as to the direction whence it has immigrated 

 into the Chagos, which at present forms its extreme western habitat. 



To sum up the foregoing : out of 23 Chagos Lepidoptera, not peculiar to this group of 

 islands, we have : — 



5 which occur in Ceylon and the Maldives and may therefore be assumed 



to have immigrated along that line. 

 1 which is Australian and which has almost certainly arrived via 

 Christmas Island and Cocos-Keeling. 

 16 which occur in Ceylon and Sumatra-Java or Australia (o£ these six are 

 found in Cocos-Keeling and two others in Christmas Island). These 

 may have come direct from Ceylon or from the Malayo-Australian 

 region, but the probabilities seem to favour the latter route since 

 none of them have been found in the Maldives. 

 1 whose range is insufficiently known. 



23 ... Total. 



COETIVY. 



ITiere are no species peculiar to the Indian, Indo-Australian, or Australian regions. 



Of the twenty species recorded all except six ( Chloridea armigera, Euhlemma ragusana, 

 Hippotion celerio, Hippotion aurora, Corcijra ceplialonica, Sylepta sabinusalis) have been 

 found in the Seychelles, and of these C. cephalonlca may be omitted as introduced 

 by man. The remaining five are found in the African or Malagasy regions and have 

 doubtless been derived thence. 



It is interesting to note the entire absence of butterflies in Coetivy, a condition found 

 also in the wasps and land-birds of this island. Yet Coetivy is situated at a distance of 

 only 90 miles from Platte Island, in which Dr. Abbott found at least two species of 

 butterfly, so that the absence of butterflies in Coetivy appeal's inexplicable from the 

 mere point of view of distance. A probable explanation is to be found in the fact 

 that the south-easterly wind, which blows fairly freshly and steadily from about May to 

 November, is sufficient to overcome any powers of flight from a northerly direction {i. e., 

 Platte or Seychelles) at this time of the year, whilst the north-westerly wind prevailing 

 from December to April is weaker and more fitful and also blows during the wet season, 

 so that any bird, wasp, or butterfly blown offshore from the Seychelles in a southerly 

 direction during that period woidd probably become rain-clogged and drowned before it 

 had gone very far. Cyclones are also of rare occurrence in this area. Whetlier the 

 theory here advanced is correct or not, it may be useful to draw attention to the 

 influence of rainfall in diminishing the dispersal-capacity of a prevailing wind. 



