132 



Isochromatous Lepidoptera. 



By J. JENNER Weir, F.L.S., F.Z.S., etc. 



Read February 23^^, 1893. 



Since November 21st, 1861, when the late Mr. Bates read before 

 the Linnean Society his memorable paper on the " Insect Fauna of 

 the Amazon Valley," in which the theory of mimetic resemblance 

 was first brought to the notice of the scientific world, many entomo- 

 logists of eminence, notably Mr. Roland Trimen, have shown that 

 protected or non-edible species are closely mimicked by other 

 species, belonging to families or genera which are preyed upon by 

 certain mammalia, birds, and reptiles. It may, indeed, be said that 

 the theory of mimetic resemblances may be considered to be estab- 

 lished, and that palatable species are aided in their struggle for 

 existence by resembling those that are unpalatable. 



There is another class of facts of a similar character the explana- 

 tion of which is not so easy, and which formed the subject of discus- 

 sion between the present writer and the late Mr. Bates. There are 

 both in the old and new world several species of butterflies belonging 

 to the same protected sub-families, or even different sub-famihes, 

 which resemble each other in both colour and markings in an almost 

 perfect manner. It cannot here be said that the edible insect 

 mimics the inedible, for all are equally unpalatable ; nor does it 

 seem possible to say which is the model, and which is the mimic. 



Mr. Moore, in his excellent monograph of the Limnaina and 

 Euploeina {vide Proc. Zool. Soc, 1883), has given tables showing that 

 there are often three, and sometimes even four, species belonging 

 not only to different genera, but to distinct groups of the Euploeina, 

 which are more or less isochromatous both in colour and markings ; 

 and there are also some instances in which the Limnaina have the 

 same resemblance in colour to the Euplceina, as true mimics have 

 to their models. 



Sometimes, indeed, the resemblance is that of true mimicry, as 

 when the females of the Euploeine genus Trepsichrois resemble the 

 species of the Limnaine genus Tirumala, because these females 

 show a complete departure from the more normal coloration of the 

 Euploeina ; it is, perhaps, needless to add that both the Limnaina 

 and Euploeina are divisions of the great sub-family commonly known 

 as the Danainse, and are, so far as known, equally inedible. 



To illustrate the foregoing observations I have brought for exhibi- 

 tion some specimens of perfectly isochromatous Euploeine butter- 

 flies, belonging not only to distinct genera, but also to distinct 

 groups : — 



Crastia core, N armada coreoides, and Pademma kollari, the species 

 exhibited, are as nearly identical in colour and markings as can be 

 conceived, even, in each species, to the duplication of the lowest 

 sub-marginal whitish spot on the upper wings ; the first has a faint 



