Thecla inorata Grote and Rob., Trans. Am. Ent. Soc, i, 323-4; 

 lb., Dcscr. Amer. Lep., in, 1-2. Saund., Can. Eutom., ii, 61-64. 

 Thecla Edwardsii Saund., ms.i 



Thecla Falacer Harr., Treat. Ins. inj. Veg., Ed. 1862, 276. 

 Scudd., pal's, Proc. Ess. Inst, iir, 1G4; lb., Proc. Bost. Soc. Nat. 

 Hist., XI, 378; lb.. Trans. Chic. Acad. Science, i, 331. 



Thecla calanus GrotQ diXidi Rob., Trans. Am. Ent. Soc, i, 172-3, 

 324^ lb., Descr. Amer. Lep., ii, 2-3; in, 2. 



On Asymmetry in the Appendages of Hexapod Insects, 



ESPECIALLY AS ILLUSTRATED IN THE LePIDOPTEROUS GeNUS 



NisoNiADES. By Samuel H. Scudder and Edward 

 Burgess. 



A conspicuous feature in the structure of the higher animals is 

 their bilateral symmetry — the tendency of the organs and frame 

 work to exact reverse repetition upon either side of a longitudinal 

 axis. 



This bilaterality is also shared to a certain extent by some of the 

 lower animals, and is generally more noticeable in the external con- 

 figuration of the body than in the internal oi^ans; it is apparent, not 

 only in those portions of the body which are disposed in pairs, but 

 also in the central organs, the opposite sides of which repeat each 

 other inversely. 



In the lower animals the exceptions to the law of bilateral sym- 

 metry are frequent and conspicuous, the shells as well as the bodies 

 of mollusks often aifording striking examples. Among the higher 

 animals, at least in the exterior sculpture of the body, cases of abso- 

 lute asymmetry are rare; the most prominent instance occurs in the 

 mature flounders; others are well known, such as the very uneonal 

 development of the tusks of the narwhal, and the two sides of the 



