236 [October, 



the fact quoted by Mr. Distant from B. Seemann's " Flora Vitiensis," 

 p. 161 (1865-73) that it had been recorded from Eromanga, the New 

 Hebrides, and the Tongan and Society groups, " probably introduced 

 as not known to the older botanists," seems to show beyond doubt 

 that it was there at that time awaiting the arrival of the butterfly. 

 Besides the introduction of the plant by man, intentional or otherwise 

 (as in the case of New Caledonia, ante, p. 189), it is in itself eminently 

 adapted for dispersal by natural agencies alone. The seeds are very 

 minute, and enveloped in a mass of silky down or cotton of the finest 

 and lightest texture, capable of being blown, if not across the entire 

 width of the great oceans, still for hundreds of miles before the strong 

 and steady breezes of the intertropical regions. In one way and 

 another Asclepias curassavica has already nearly completed the circuit 

 of the globe, if indeed it has not already done so. 



Thus it would appear that human agency has played not a primary, 

 but at most a secondary part in the dispersal of Danaida plexippus. 

 Many a time since the butterfly became established in North America 

 — possibly soon after the glacial epoch — individuals or small companies 

 have been carried with the aid of the winds to far distant lands, but 

 these pioneers, failing to find suitable food for their progeny, have 

 perished without continuing their race. With the great increase of 

 communication with the Pacific Islands and coasts which commenced 

 before the middle of the last century, this deficiency has been supplied, 

 and we now find Danaida plexippus ranging over a greater extent of 

 the earth's surface than any other butterfly, with one possible ex- 

 ception. Probably, too, it is only a question of a few years before vast 

 areas in Asia and Africa, to all appearance as suitable to its existence 

 as those it has already occupied, will be colonized by this bold and 

 enterprising insect. 



With regard to the probability or otherwise of our butterfly 

 becoming established in Europe, I have personally no doubt as to its 

 finding, on the shores of the Mediterranean, a climate and environ- 

 ment eminently suited to its requirements, in the event of its reaching 

 that region under favourable conditions at any future time. Even if 

 Asclepias curassavica, which, as we have already seen {ante, p. 193), had 

 more than twenty years ago spread as far as the Suez Canal, should 

 from any cause fail to obtain a footing farther westward, an acceptable 

 food-plant is available in the closely allied Gomphocarpus fruticosus. 

 This plant, widely distributed in Africa, is also found in Syria and 

 Asia Minor, and I saw it many years ago growing freely in the region 



