NATURAL COLONISATION METHODS 295 



appear that there is a southern return current, for a bottle, 

 launched in Mauritius, is said to have reached the atoll. But 

 I do not think that this is a possible route for colonists, for the 

 bottle almost certainly came to the atoll from the eastward, 

 after completing an enormous circuit of the Indian Ocean. 

 The length of this journey would almost certainly prohibit the 

 success of the route as a path for colonisation. Upon the 

 experiment of the drifting bottle, we may base some calcula- 

 tion as to the time which would be occupied by an animal 

 floating from the nearest land to the atoll ; and we may reckon 

 that, if the strength of the drifts to the east and to the west 

 of the atoll are at all comparable, a colonist must face a sea 

 journey of some forty days. During a stay of a fortnight in 

 October 1906, in a ship lying on cable ground some twenty 

 miles south of Sumbawa, the current flowed constantly 

 westward at the rate of about one and a half knots ; and the 

 waters were carrying all sorts of drift wrack in their stream. 

 If this rate were to be maintained, the time of the journey 

 would be reduced to a half ; but the near-shore currents are 

 subject to variations, for the region is one affected by the 

 monsoon. The atoll itself, however, lies without the mon- 

 soon area, and the steady westerly drift is apparently constant 

 throughout the year's cycle. 



Several creatures must have survived this perilous 

 journey of almost two months of clinging to some floating 

 thing. There are several instances of large snakes having been 

 killed in the atoll, and others have been picked up on the 

 beach, where the waves have cast their vessels. There are, 

 preserved in the Governor's house, the skulls of two crocodiles, 

 shot after successful colonising : and these colonists must have 

 used this route. Of the permanent additions to the island 

 fauna we must probably reckon Typldo'ps Iraminus, the one 

 earthworm, some of the coleoptera, and perhaps the millepedes 

 which live in rotting wood. Of the flora that has been assisted 

 by flotsam, the fungi are of most interest; and, as throwing 

 some light upon their means of dispersal, it is important to 

 note that every one of the eight species established in the 



