84 THE entomologist's recokd. 



any particular shape or pattern, and, at a very short distance, become 

 obliterated. Coupled with the transparency, it is to be noted that they 

 carry the abdomen held far back into the hmd wings, and thus render it 

 doubly difficult for any enemy to deliver attack successfully. This habit 

 of raising the abdomen has spread into almost all the Ithomiine genera, 

 besides some Danaines and Heliconiines, where transparenc}' has not 

 yet been developed. In case (2), already referred to, Batesian mimics 

 or cases of protective resemblance are extremely varied. Besides hawk- 

 moths being like bees, Sesiids, Syntomids and Arctiids, like flies, 

 gnats and wasps, we have Acra^as, which resemble their sandy sur- 

 roundings, and it becomes tolerably clear how, in the first place, the 

 insects we term the models in a protected group assumed transparency. 

 There are, however, certain cases which do not readily suggest an 

 explanation. Why should a rapidly-flying Hesperiid, such as Knthen^ 

 ritren^, be developing transparency ? It is more than likely that before 

 it became transparent it had an already extremely rapid flight, as have 

 its completely-scaled near relatives. Again, why should the Erycinids 

 of the genus Zeonia be transparent? They are extremely conspicuous 

 when at rest on a leaf with all the wings spread out, and on the wing 

 they are so swift that it is impossible to follow them. Has their 

 rapid flight been accelerated by a loss of scales ? Possibly it has, yet 

 the near relatives of the genus Diurrhina also have a very rapid flight, 

 and are almost completely scaled. Some members of Diorrhinaduve, how- 

 ever, developing a transparent tendency. It would be scarcely possible to 

 say if one or other were the faster unless the diflerence be very great, but 

 there is a possibility that a small advantage gained by the diaphanous or 

 semi-diaphanous species is sufficient to be a help in the struggle 

 against enemies. While it is possible to account for some cases of 

 transparency, it is very obscure, in other cases, what could have given rise 

 to diaphanous wings, more particularly wings that have patches only 

 transparent, unless they are thereby made more eft'acive at a short 

 distance than they otherwise would be, or are in a transition stage to 

 complete transparency. The Syntomids, Aijyrta intcilia, Anyrta dux, 

 or Knoiira codestina, are certainly not at all inconspicuous when on the 

 wing, and, if one of these has been a model, as one surmises, it has 

 been one to which species might converge ; but there does not appear 

 to be any plausible argument as to why this special characteristic 

 should have become so marked. It is probable, however, that once 

 other species had been brought within the influence of the dominant 

 species, whichever it was, that they, by their especial structure, could 

 become more transparent than their model, and that what was 

 originally a not very marked feature became developed by the action 

 of mimicry. I utterly fail to see how Mr. A. H. Thayer's theory of 

 effacive coloration (Trann. Ent. Soc. Loud., p. 53B, 1908) can apply 

 to the brilliant coloration of Aj/i/rta micilia, which is as brilliant on 

 the wing as in the cabinet. 



To look at some other Syntomids we And the case very difierent. 

 In British Guiana, Aethria leiicaspis, Aethria daltha and Seslura 

 sinarandiiia fly together in the sunshine, their resemblance to one 

 another being extraordinarily close, and one immediately regards them 

 as a Miillerian group, with one or other as the dominant member, 

 dominant by being most distasteful and most abundant. That 

 member is undoubtedly Aet/nia lcticofi}iis, as the proportion of each 



