in the Hind Wing of Catocala, Schr. 447 



Agrotis pronuha^ Linn,, to the small Agrotis anachorefa, 

 H.-Sch., and luper'moides, Gn. The hind wings of these 

 small species of Agrotis are not less brightly and conspicu- 

 ously coloured ; and even granting that this feature in the 

 case of the first-mentioned species (the Large Yellow Under- 

 wing) is able to divert the attention of a bird so as to cause 

 it to attempt to seize the insect bj its hind wings, this would 

 still be far too difficult in the case of the two latter species 

 when on the wing, owing to their very smallness. It would 

 undoubtedly be easier for the pursuing bird to strike at the 

 lody. But even if we admit the justice of this explanation in 

 the case of Agrotis pronuha, Linn., it is still impossible to fix 

 a limit up to which the yellow coloration of the hind wing 

 may be injurious to the possessor or to decide when its 

 attractive property may begin to be useful to the insect, for 

 species of Agrotis occur in all sizes in an ascending series 

 from the smallest forms. It must also not be overlooked 

 that, in opposition to the large species which, apart from 

 accidental contingencies, flies exclusively by night, we find 

 the above-mentioned small species of Agrotis on the wing by 

 day, and therefore at the only time when they are in a 

 position to turn the yellow coloration to account. 



It we are unwilling to admit the force of all these state- 

 ments, there still remains the question as to how we are to 

 reconcile with the principle of attractive wing-coloration the 

 bright colour of the body of various species of Catocala {pacta, 

 Linn., neogama, Sm. Abb., magdaltna, Streck., Frederici^ 

 Grote, neonymj)ha^ Hbnr., and arnica, Hbnr.), of Agrotis 

 jimhria, Linn., &c. ; for since the wings, which during flight 

 are in a state of rapid movement, appear less brilliant than 

 the similarly coloured body, which is more at rest, we are 

 led, on the basis of the above-mentioned principle, to the 

 conclusion that this brighter body is calculated to entice 

 birds to pursuit. Furthermore, how can the black marking 

 of the hind wing be consistent with the recognition of this 

 principle? Since, by virtue of well-known physiological 

 laws, the parts of the wing that lie nearer to the base and 

 move with less great rapidity appear brighter to us than the 

 marginal portions of the wing, it follows that the former, 

 which are adjacent to the bod}', must, being the brighter, 

 concentrate the attention of the pursuer upon themselves. 

 This concentration of the attention is further accentuated and 

 the capture of the fugitive moth thereby facilitated if the 

 margins of the wings are darkened, so that the lightness of 

 the central area is heightened by contrast ; and it is actually 

 a fact that, in the case of the species of Agrotis with yellow 



