184 



Dr. A. Jefferis Turner's Observations on 



the cossid areole and chorda have been lost, but the media 

 has been retained, in the Noctuidae, Arctiadae, Liparidae, 

 and Notodontidae the former have been retained and the 

 latter lost. It follows that the descent of the second group 

 of families from the first is an impossibility ; they have 

 developed from the cossid stem by a separate branch. 

 How far this applies to those families which have lost both 

 structures I will not inquire at present. It is advisable, 

 however, to note that although the media is not developed 

 as a vein, which occurs rarely in the higher families, it is 

 frequently represented, either branched or unbranched, by 



Fig. 53. — Monodenia fahrnaria, 

 Gn. 



Fig. 54. — Diceratucha 

 xenopis, Low. 



a fold in the wing-membrane. These folds I have not 

 reproduced in my diagrams. 



Thyatiridae (Cymatophoridae). — The explanation that I 

 have given as to the fate of the areole in the Lasiocampidae 

 is to some extent supposed by the analogous structure in 

 the Thyatiridae. As Sir George Hampson has pointed out, 

 the areole in this family is frequently not closed, the varia- 

 tion occurring rather frequently in the limits of a single 

 species. There does not appear to be here any instance 

 of the development of a new structure, which would be 

 shown by a gradual change in a series of related genera, 

 but of the loss of part of a structure in a proportion of 

 individuals of a species perhaps owing to the absence of 



