Eastern Pieridce. 3 1 1 



interesting to find, however, tliat dimorphism, which is so strikingly 

 developed among the Pop'dionidce, should be represented in a 

 smaller degree in the closely allied group. 



A very curious case of close resemblance occurs between two 

 other insects, P'leris cynis and Tacliijr'is illana, which well illus- 

 trates the difference between resemblance produced by the mere 

 recurrence of a general type of colouring and that which is the 

 result of the preservation of usefid variations, and which is termed 

 "mimicry." These two butterflies are nearly of the same size, 

 of a white colour with a broad apical black border similarly scal- 

 loped within, and on the hind wings both have a similarly-formed 

 sub-macular dusky border. They differ, however, in the propor- 

 tion of the discoidal cells and in the structure of the antennae and 

 anal valves, so as to come into distinct genera, and they are not 

 found together, one being an inhabitant of the Malay Peninsula, 

 the other of the Philippine Islands. If the markings of these 

 insects had been more varied and peculiar, it would have furnished 

 one case for the opponents of the explanation of " mimicry" by 

 natural selection. As it is, however, it well illustrates the excep- 

 tion that proves the rule. By far the most general type of colour- 

 ing in the Pieridce, and which recurs in hundreds of species, is 

 a white ground with a black outer border, always most developed 

 at the apex of the upper wings, and very frequently less marked 

 on the hind wings. It is not, therefore, surprising that among the 

 many slight modifications of this commonest and most simple type of 

 colouration, two species belonging to different genera should closely 

 resemble each other externally. It is a case that exactly cor- 

 responds to the very common type of colouration among the Vara- 

 bidce, — black elytra with two or four rufous spots, — which recurs 

 so frequently in many distinct genera of that family. Such cases 

 serve to show us how completely inadequate is the law of " rever- 

 sion to a common type" to explain the resemblance, through all 

 the minute details of a complicated and unusual style of m.arking 

 and colouration, which is often found in cases of " mimicry." 



Althoush the differences of neuration offer excellent characters 

 for the establishment of genera, it is of too uncertain and variable 

 a nature to serve as a complete test of their affinities to each other. 

 I have therefore endeavoured to arrange the genera in a natural 

 series rather by the form of the antennae, which seems less liable 

 to sudden and abnormal variations, and by other general characters ; 

 commenciuG as usual with the long and slender antenn.-E of the 

 weak-flying Leptafis and Euterpe, and ending with the thick 



