PAPILIO VIII. 



is a peculiarity which Brevicauda shares only with the Asierias gi'oup. The 

 mature larva diflcrs from that of Asterias. Zollcaon, or Machnon, in the absence 

 of the yellow or orange spots which ornament those species, and the black stripes 

 are more broken. The caterpillar of Allaska is unknown, but is probably closely 

 like that o( Machaon. 



Mr. Bates, in the paper before cpioted, considered Brevicauda as a local form 

 o( Asterias, but on my pointing out the diflerences between the two, he re})lies 

 that Mr. Milne's specimens were so much damaged that a complete comparison 

 could not be made, but that on my representation, " there cainiot be any doubt 

 of Brevicauda being a good species, quite as distinct from Asterias as the Corsi- 

 can P. Hospiton is from Machaon^ 



Allaska Hies over the northern portion of the continent frou) east of Hudson's 

 Bay to the Pacific, and the range of Asterias is from Canada to Mexico and from 

 ocean to ocean. It is therefore the more remarkable that Brevicauda shoidd 

 be restricted to two islands on the coast, l»eing also excessively rare on one of 

 them, and to a limited district on the adjoining mainland. One may naturally 

 ask, how happens it that a species midway between two others which divide be- 

 tween them the continent, should be found thus restricted. Its peculiarities pre- 

 clude the idea that it can be a mere ollshoot from either of the species named, 

 for in such case, while it would agree in part with the parent stock, the points 

 of divergence would not ha just so many points of agreement Avith any other 

 species, and most especially with the only other at all allied to it which is to be 

 found in its district. The variation would take a new direction rather. 



There are two ways of accounting for this phenomenon ; first, that Brevicauda 

 has originated in hybridism between the two species named. A brood being 

 hybridized, its members have proved fertile, have increased moderately, and have 

 been prevented by segregation on the islands from subsequent intercrossing with 

 either parent stock. By this means the individuals now existing have become 

 essentially alike. Segregation again has originated and perpetuated certain 

 minor differences between the inhabitants of the two islands, as in color, those 

 on one being mostly yellow, on the other fulvous. And from the islands the 

 main-land is now colonized. 



Or, second, Brevicauda represents an ancient, dominating, now almost extinct 

 species, from which Asterias and llachaon have naturally descended, and each 

 of which, in process of time, has thrown off one and another variety, some of 

 which, favored by circumstances, have become pei-manent, and now constitute 

 the group which gathers about its intermediate stock. 



This last seems to me a reasonable and probable statement of the relationship 

 of these several species. 



