70 'WHAT IS A species:^' 



alh', regarded as sufticieiU. Some of the chief of these 

 categories are briefly set forth under the five lieads a-c. 



a. PimoypJiis))i^ Polymorphism : — In an ever increasing 

 number of examj:>les an assemblage of indi\iduals is re- 

 garded as a single species, cdthough split up into two or 

 more widely different and sharply separated groups, 

 between which transitional varieties are excessively rare 

 or even unknown. I-^or instance, the extremel\- abundant, 

 widely distributed buttertly Livnias chrysippus inchides 

 among other forms one in which the black-and-white tip 

 is wanting from the fore-wing, the do)-ippus i^ = kluQ^ii) 

 form. This variet)- is sharply cut off from the type form. 

 Although faint traces of a former white bar can be made 

 otit in doj'ippus, I have never seen, among thousands of 

 individuals, the material out of which a oood transitional 

 series between it and chrysippus could be constructed. 

 In this case the evidence of S^ngam)- is strong and com- 

 plete ; for Col. \'erbury has recorded the fact that the 

 two forms certainly occur iii copula \ Pnit even if this 

 record were wanting there would still be strong presump- 

 tive evidence that the forms are associated by S\ngamy 

 and Epigon)'. Thus, so far as our knowledge extends, 

 ciorippus occurs as the only form in certain parts of 

 NE. Africa alone. Erom this, its metropolis, dorippus 

 spreads on all sides, its individuals existing intermingled 

 with those o{ chrysippus, becoming less and less numerous 

 until the)- fmall}- die otit. Thus if we trace the two 

 forms eastward we fmd them both abundant at Aden : 

 further east, at Karachi, dorippus is well known, but very 

 scarce as compared with chrysippus \ in Southern India 

 it is a great rarity, if indeed it is known at all on 

 the mainland ; in Ceylon a single specimen was cap- 

 tured by Col. Yerbury in 1891, and since then others 

 have been taken. ^ Further east I have never heard 



* Speaking of his experience at Aden, Col. Verbury says: 'I have 

 taken ihem [the forms o{ chrysippus^ " in coitu " in every possible combina- 

 tion' {Jouru. Bomb. Naf. Hist. Soc, vii (1892), p. 209). 



' See Major N. Manders, F.Z.S., in Journ. Bomb. Nat. Hist. Soc, xiv 

 (1902), p. 716:— 



'The first specimen of this insect \^(iorippus-=.klui^ii\ in Ceylon was 

 captured by Lieut. -Colonel Yerbury at Trincomalic, April 15, 1891 . . .' 



