12 



nilOPALOCEIiA M. ! i 1 \ J A'. I . 



Besides this species, which is found in Europe, and which does not occur much above 

 41" N., there is also an American species, which extends throughout the length of its tropical 

 regions, and is found as far north as Canada. Mi\ Bates * acutely observes that it is 

 interesting to rind that this, the only genus of the ihinuinw which is common to the three 

 tropical regions, is the sole one of the subfamily that occurs in high latitudes. And further 

 that "the only means of communication between the intertropical lands of America and Asia 

 seems to have been a circuitous route by the north (or south) ; and the essentially tropical 

 forms do not appear to have passed along it." This American species, however, has in quite 

 recent times, become (and the process seema still going on) distributed through many of the 

 Pacific Islands, to New Guinea and Australia, and has even been found in Europe, which 

 its previous appearance at the Azores had somewhat rendered probable. A few years ago f 

 I endeavoured to trace the course and cause of this migration, and had reason to come to the 

 conclusion that its distribution was apparently governed by the range of its food-plants, which 

 are species of Asdepias, and that the directing causes were probably due to the accidental 

 agency of man in the first place, and possibly also to prevalent winds and currents. 



It has been well pointed out by Mr. Wallace that the most widely distributed species are 

 probably the most ancient, and it will particularly apply here, if we qualify that statement by 

 the proposition made by Dr, Buchanan White, J that unless circumstances {not necessarily 

 or always some form of human agency, as Dr. White apparently relies upon) have been 

 exceptionally favourable, species which have the widest distribution are probably of greater 

 antiquity than those whose distribution is less extensive. The most widely distributed species 

 of Danais is D. chnjsippus, the species to which we have alluded as even occurring in S»E, 

 Europe, and which is of a similar tawny hue to the American IK pUxtppus, which has also an 

 exceedingly wide habitat (though probably recent in extent of distribution), and likewise occurs in 

 high latitudes. All the tawny species of the genus with which I am acquainted have, also, but 

 one subcostal nervule emitted distinctly before the end of the discoidul cell ; and therefore, if 

 we accept these tawny species as representing the original colour of the genus, we may also 

 ;u:o. ]'L this as the primitive neuratiom This view receives apparent confirmation from 

 observing that it is amongst the green -spotted species that we find the second subcostal 

 nervule emitted before the end of the ceil, thus leading on to Eademt, Idcopsis, and Hestm in 

 that respect; but which last-named genera take a fresh departure in having the first subcostal 

 nervule anastomosed with the costal nervure. This also appears concurrent testimony to the 

 views of Mailer to the same effect, and which we have previously endeavoured to convey (ante, 

 p, 3). In a curiously marked East African species in which the tawny and green -spotted facies 

 are combined, and which was lately described by Mr. Godman, § a fresh departure is taken 

 from the ordinary type by the first and second subcostal nervule s being anastomosed. 



The males possess on the posterior wings one or more dull -coloured patches, situated on 

 or in the neighbourhood of the third median nervule and submedian nervure. These were 

 long known only as "sexual spots," but Muller|| has ably and strongly shown that they are 

 really scent-producing organs. They are, indeed, glands or pouches, but as they open only by 



* Trans. Linn. Soo M vol. xxiiL, p. 405 tt *etj. (1862). | Trans. Eut, Soc. 1877, p. 98. 



{ ' Entomologist/ vol. xiv„ p, 270 (1881 j. £ Pruc. Zuol. Soc, 18S0 T p. 183. 



|| Trans. Ent. Soc., 1878, p. 21S. 



