1970] 
Burns — Erynnis 
431 
1963) suggest the following general explanation. In the course of 
differentiation, cells destined to produce the left valva were damaged ; 
and the organism regulated with a contribution from corresponding 
cells of the right side. These were already determined for right 
valval morphology. But, in their new location on the left, they 
made a structure that assumed the proper functional orientation. 
Thus a mirror image of the right valva emerged. 
Regulation of this kind, detectable when it overturns asymmetry, 
would never reveal itself in most species because the genitalia are 
symmetric from the beginning. 
Acknowledgements 
I thank M. P. Kambysellis and J. H. Postlethwait for reading 
the manuscript, and R. G. Gillmor for drawing the figures. This 
work was supported in part by grants from the National Science 
Foundation (GB 5935) and the William F. Milton Fund of Har- 
vard University. 
Literature Cited 
Burns, J. M. 
1964. Evolution in skipper butterflies of the genus Erynnis. Univ. 
California Publ. Entomol. 37: 216 pp., 1 pi. 
Evans, W. H. 
1953. A catalogue of the American Hesperiidae indicating the classi- 
fication and nomenclature adopted in the British Museum (Na- 
tural History). Part III. Pyrginae. Sec. 2. London: British 
Museum. 246 pp., pis. 26-53. 
Scudder, S. H. and E. Burgess 
1870. On asymmetry in the appendages of hexapod insects, especially 
as illustrated in the lepidopterous genus Nisoniades. Proc. Boston 
Soc. Nat. Hist. 13: 282-306, 1 pi. 
Ursprung, H. 
1963. Development and genetics of patterns. Am. Zoologist 3 : 71-86. 
Figures 1-4 follow 
