IV. 



slightest doubt of the absolute distinction of the two common 

 Plebeiids, Plebeius argus (aegon) and P. argyrognomon, throughout 

 the whole range of their distribution ; their parallelism in superficial 

 appearance is remarkable, but their structural characters are most 

 definite and absolute, and leave no justification for Staudinger's 

 statement that in certain districts they were still not properly 

 differentiated as species. 



An important point that has influenced the smaller number of 

 species with which we have been able to deal in this volume, is that of 

 the illustrations. Thanks to the energy and generosity of Dr. T. A. 

 Chapman, we have been supplied with a large number of photographs 

 of biological details, mounted by himself and reproduced by Mr. F. 

 Noad Clark, to illustrate his section of the work. In addition we 

 have also to thank Messrs. Hugh Main and A. E. Tonge for further 

 photographs dealing with the early stages of the species treated. We 

 have also received large numbers of figures and photographs of aberra- 

 tions of the different species which we have, as far as possible, utilised 

 in our illustrations of the imagines. Some of these have, and others 

 have not, been published previously ; we have selected from those sent 

 the figures that best illustrate the points of variation discussed, and 

 thank the various donors for their kindness. The publication of some 

 53 plates has somewhat lessened the space at disposal for letterpress, but 

 this still comes to more than 400 pages, although to get as much 

 systematic work in as possible, we have reduced the preliminary 

 chapters to 3, which, however, complete our series of essays on 

 " Family habits in butterfly larvae." 



On the literary side of our work we have received equally important 

 aid. To Mr. G. Bethune-Baker, Professor Charles Blachier, Mr. H. 

 Rowland-Brown, Mr. Stanley Edwards, Mr. Max Gillmer, Dr. J. L. 

 Reverdin, Mr. Alfred Sich, and the Rev. George Wheeler, our most 

 sincere thanks are due ; to Mr. Stanley Edwards we owe so much that 

 it would have been impossible to have completed this volume in half 

 the time had he not acted as a most able amanuensis and extractor, 

 obtaining from the old authors in the museum libraries, excerpts which 

 we ourselves could never have hoped to have spared time to obtain. 

 Although we have lost our Hungarian colleague by the lamented death 

 of Mr. Aigner-Abafi of Buda-Pest, we have received a promise of help 

 from the well-known Croatian entomologist, Mr. August Grund, so 

 that our knowledge of the eastern forms of our insects is not likely to 

 be in any way lessened, but rather increased by his kind co-operation. 



Mr. Heron has, as usual, made our work at the Natural History 

 Museum as effective as possible, by helping us to make the most of 

 the limited time at our disposal when there, whilst Mr. H. J. Turner 

 has again kindly undertaken the compilation of the " Synopsis of 

 Contents" and the "Special Index," In a work of this scope and 

 magnitude, reference to almost any particular detail will show that 

 other helpers have never been wanting, and it is by the kindness of 

 these that the production of the volume in its completed form has 

 been made possible. 



We hope our subscribers will not be dissatisfied with the contents. 

 Another volume will take the rest of the Lycaenids and Erycinids, 

 after which, one may suppose, there will be, among the larger butter- 

 flies, less field for quite new work and new discoveries, and less room for 

 the thankless task of critical scold to earlier workers in the same field. 



