169 



this instinct in that great economy that we call Nature, one of the 

 safety-valves, or to express more properly, one of the compensation 

 •weights of that mechanism, that prevent a species getting too 

 numerous and superseding their neighbors and contemporaries in 

 creation. 



Amongst the Lepidoptera, I know df very few instances of real 

 migration, and on a later occasion, I shall state those few instances ; 

 but that instinct to seek a current of air, and to strive on against 

 it, is very generally spread to that whole class. This instinct or 

 law of nature compels, not only its victims to drown themselves ; it' 

 also forces them up to the summit of mountains, and to freeze to 

 death there, far above the boundary of all vegetation, in the soli- 

 tude of an irrespirable rarified atmosphere. It is especially the 

 group of the Pierides and true Papihonides that long for this most 

 romantic death, and it is one of the most curious, and in the first 

 time, unaccountable sights, to witness, in a solitude of snow, and on 

 a barren rock, swarms of brilliant Butterflies, glowing in all the 

 brilliant coloration of the tropics. 



The genus to which our Danais belongs seems not to be subject 

 to this dangerous propensity. The Danais, with her congeners, 

 Euploea and Heliconia, shun the mountains, and seem to affect sea- 

 coasts. These butterflies frequently are to the sailors bearers of 

 terrestrial welcome, before the coast is seen ; and I think the Asi- 

 atic genus Euploea, bears its name from this peculiarity. I con- 

 sider the name derived from Eu, " well," and Ploion, "vessel," well, 

 meaning to navigators ; or it may be derived from Eu and Pleo, " I 

 navigate," and means an inseet that is a good navigator. In this 

 case it is the current of cold, densified air that by its specific 

 weight, presses back the extended, and by heat, rarified atmosphere 

 of the tropical lowlands. A current of cool air is daily rusliing 

 down certain gulches, and they are the very same gulches that are 

 most frequented by those Lepidoptera we ar& to meet beyond the 

 limits of vegetation. 



Danais evidently is also a good navigator — without such nautical 

 talents it never would have reached Honolulu ; and this accounts, 

 perhaps, for its extensive geographical distribution. 



