EXTERNAL ANATOMY OF INSECTS. 647 



however that in many Lepidoptera the wings are partially, 

 and in some instances generally, transparent : thus in 

 Hesperia Proteus, a butterfly before noticed for the long 

 tail that distinguishes its secondary wings, there are many 

 transparent spots ; in Attacus Atlas, one of the largest 

 of moths, and its affinities, there is as it were a window 

 in each wing formed by a transparent triangular space ; 

 in A. Polyphemus, Paphia, &c, the pupil of the ocellus is 

 transparent, which in the former is divided by a ner- 

 vure. In several of the Heliconian butterflies, and in 

 Zygcena F., &c, the greater part of both wings is trans- 

 parent, with scales only upon their nervures, round their 

 margin, or forming certain bands or spots upon them ; 

 in Parnassius Apollo, Mnemosyne, &c, the scales are so 

 arranged as not wholly to cover the wings, which renders 

 them semidiaphanous; and in some (Nudaria) the wings 

 are intirely denuded. "With regard to size, the scales vary 

 often considerably in different ti'ibes; in Heliconia they 

 appear to be more minute than in the rest ; and in Cas- 

 tnia they are the largest and coarsest; the extremity of the 

 wings of Lepidopterous insects in general is fringed with 

 longer scales than their surfaces, and even those of the last 

 in the same wing sometimes vary in magnitude. The little 

 seeming tooth that projects from the middle of the pos- 

 terior margin in the upper wings oiNotodonta, a subgenus 

 of Bombyx L., is merely produced by some longer di- 

 verging hairs. The shape and Jigure also of scales are 

 very various — some being long and slender ; others short 

 and broad ; some nearly round ; others oval, ovate, or 

 oblong ; others spathulate ; others panduriform or para- 

 bolical ; some again almost square or rhomboidal ; many 

 triangular ; some representing an isosceles triangle, and 



