PAPILIO VJII. 
is a peculiarity which Brevicauda shares only with the Asterias group. The 
mature larva differs from that of Asterias, Zolicaon, or Machaon, in the absence 
of the yellow or orange spots which ornament those species, and the black stripes 
are more broken. The caterpillar of Aliaska is unknown, but is probably closely 
like that of Machaon. 
Mr. Bates, in the paper before quoted, considered Brevicauda as a local form 
of Asterias, but on my pointing out the differences between the two, he replies 
that Mr. Milne’s specimens were so much damaged that a complete comparison 
could not be made, but that on my representation, “ there cannot be any doubt 
of Brevicauda being a good species, quite as distinct from Asterias as the Corsi¬ 
can P. Hospiton is from Machaon A 
Aliaska flies over the northern portion of the continent from 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 should 
be restricted to two islands on the coast, being 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 offshoot 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 be just so many points of agreement with 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 Machaon 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 permanent, 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. 
