( cxxv ) 



Among the Heterocera that fly in more or less of obscurity 

 I think it may be said that the majority of species exhibit 

 variation in colour and pattern of a kind and degree sufficient 

 to arrest the attention of any observer duly endowed with 

 sight. The range of variation in the numerous polymorphic 

 species which, for a reason subsequently given, I call indis- 

 criminately polymorphic, is enormous, and fully justifies the 

 remark frequently met with in the books that, " take them 

 where you may, there are scarcely two alike." I give some 

 examples in a note.* 



I think it will be found that the indiscriminately polymorphic 

 Noctuse usually conceal themselves by day in grass and low 

 herbage or in thatch, faggot stacks, ivy, &c., and do not rest 

 by day, on palings, &c., where, indeed, many of them would be 

 quite conspicuous. Still, they fly long before it is very dark, 

 and the whitish underwings with which many are furnished, 

 and which ai-e displayed in flying, greatly add to their 

 conspicuousness. And there must be some eyes capable of 

 stealing upon them in their daytime retreats. 



Discriminate polymoiyhism. 



There are two classes of cases in which polymorphism would 

 appear to be distinctly advantageous. The first consists of what, 



pee Packard's "Text Book of Entomology," pp. 249-64 ; also Dr. Sharp's 

 Presidential Address, Proc. Ent. Soc. Lond. 1888, pp. 1-lxvi, and his 

 paper. Trans. Ent. Soc. Lond. 1889, pp. 393-408. Many perceive light 

 beyond the violet rays which bound our vision. As to the capacity of 

 moths for seeing in obscurity, every moth-collector must have observed the 

 glowing eyes of 



" . . . . the filmy shapes 



That haunt the dusk, with ermine capes 



And woolly breasts and beaded eyes." 



As regards vertebrate enemies there is no doubt of the keen seeing power of 

 these, many of them, such as owls and some other birds and other nocturnal 

 animals, possessing special adaptations for use in obscurity. 



* Apamea didyma {oculea) exhibits any shade of ground colour from 

 pale whitish grey to black ; of the pale ones some have a dark costa, 

 others a conspicuous dark central band ; none are described as restricted to 

 any particular locality. Thirty forms are enumerated and described in 

 Tutt's "British Noctuae," vol. i, pp. 91-94. Miana strigilis, Agrotis 

 tritici, Agrotis cxclamationis, Noctua f estiva ("I have at times possessed 

 hundreds of specimens, of which I can truly say that no two were alike." — 

 Humphrey and Westwood's "British Moths," p. 124). Triphxna pronuba, 

 and among Geometrid moths Hypsipctes elutata, of which Barrett writes : 

 " Excessively variable, the colour ranging from green to brown and endless 

 variety in the marking." 



