J. W. Douglas's Note on Segetia Xantliographa. 99 



XXVI. Note on a Variety of Segetia Xanthographa. (PI. 

 XIV. fig. 1.) By J. W. Douglas, Esq. 



[Read 6th March, 1848.] 



At the meeting of this Society on November 1st, 1847, I exhibited 

 a most curious specimen of this moth, taken near Manchester, and 

 sent to me by Mr. Edleston, On the right side the wings present 

 the usual appearance of the species, but on the left the upper wing 

 has only a broad stripe of brown on the costal portion, the rest 

 of it being luteous, with a few dark marks, and the lower wing 

 being dark, with a broad luteous dash running down the centre. 

 It is a most singular deviation from the normal appearance of this 

 moth, and has been most ably drawn by Mr. Wing, to whose figure 

 I beg a reference, as giving a better idea of the insect than any 

 description I can make. 



What may have been the cause of this variation I am unable to 

 say decisively, but some observations reported to the Entomolo- 

 gical Society of France by M. A. Pierret,* will, I think, throw 

 some light on it. He says, that of several species of Lepidoj)tera 

 which ordinarily have the wings red, varieties occur in which that 

 colour is replaced by yellow. He instances Sphinx Dahlii, S. 

 Euphorbice, Zygcena Achillea, Z. Fausta, and Z, Onobrychis, Eu- 

 chelia Jacobece, Chelonia Caja, C. Hebe, and C. purpurea, Calli- 

 morpha Hera and C. dominula. He says the reverse of this never 

 takes place, with the single exception of Callimorpha donna, in 

 which the yellow of the under wings is sometimes replaced by 

 red ; but in this case he thinks, that as C. donna is really only a 

 variety of C. dominula, the apparently accidental red is properly a 

 return to the typical colour. He then concludes, that every yellow 

 variety of a red type is caused by an arrest of the elaboration of 

 the colouring matter of the perfect insect, resulting either from 

 the imperfect or improper nutrition of the caterpillar, or from the 

 influence of atmospheric agents while in the pupa state. 



I think that if this theory be correct, that it may account for 

 the variation of the species now before us, although this differs 

 from the examples quoted by M. Pierret, inasmuch as the typical 

 colour is not red, and the yellow variation is on one side only. 



* Annales de la Societe Entomologique de France, 1847. Tome 5, Bulletin, 

 page Ixxii. 



VOL. v. O 



