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found being Naples. The insect is equally common on the Cape 

 Verde Islands as in Manila, Adelaide, etc., but it is an interesting 

 fact, and worth mentioning, that the Sandwich Islands possess our 

 American, and not the Gerontageic and Polynesian species D. 

 chrysippus. I account for this anomaly in its geographical distri- 

 bution, by considering the Sandwich Islands archippus a Califor- 

 nia colony. We see through our whole Summer and Autumn our 

 Danais in the very streets of the city, struggling against the west- 

 ern gale that sweeps this peninsula. The food of the caterpillar 

 consists extensively of plants of the Asclepias family. Our bot- 

 anical members know best that the nearest habitat of any of 

 the plants, is on the other side of the bay ; so that evidently the 

 brown-winged visitors are an immigration. And really in crossmg 

 the bay you may observe frequently the uncouth but powerful flight 

 of this large butterfly, always in an easterly direction. There is 

 a great gathering of this Danais on the outer Telegraph Hill, and a 

 considerable number is constantly seen sea-faring themselves out 

 on the Pacific. 



Now it is my opinion that somehow or other single individuals, 

 favored by concurring circumstances, may have reached, and 

 reach now these distant islands, and be the founders and maintain- 

 ers of this unexpected colony. For instance, they might get into 

 a strong northerly breeze, get carried by that into the trade-winds, 

 and amongst hundred thousands, perhaps one pregnant female may 

 chance to alight on an island, deposit her eggs on some of the 

 Asclepias family, with which group of plants the islands are well 

 stocked, and the colony is there. If the Gerontageic and Polynesian 

 species Chrysippus exists on the Sandwich Islands, I do not know» 

 I always received from there Archippus. It remains now to ac- 

 count for that singular propensity of an insect species to get drowned 

 in the Pacific. 



There seems to exist a law in the animal kingdom that compels, 

 not only single individuals, but extensive flocks, to strive against 

 a current, may it be one of water or of air. Dr. Ayres, our Ichthy- 

 logical friend, will have observed that instinct frequently hi fishes, 

 and there it seems to have a cause, namely, to keep a station, or a 

 certain range, that would be immediately lost if the animal would 

 trust itself to the current. More difficult it is to account for this 

 instinct in certain insects, that by that very propensity are carried 

 to locahties, where the individual perishes without propagating the 

 species. It appears to me that this instinct has the same cause 

 that compels certain Mammalia, of the family of the Glires, for in- 

 stance, the Norwegian Lemming, by wandering in one straight line 

 to seek a destruction that they are pretty certain to meet. It is 



