THE LEPIDOPTERA OF PERTHSHIRE. 73 



teut use them for our own convenience; a genus such as Dr. 

 Staudiuger's Agrotis, with 170 European species in \t, is an 

 evil in itself, — Ave cannot always define even the limits of 

 species; and this leads me to a very important feature in the 

 Catalogue before me. Our author has adopted in it Dr. Stau- 

 diuger's plan of arranging varieties under different heads. 

 Long ago, Mr. Wollaston laid it down as an axiom, that " a 

 variety, to be technically such, must have in it the prima 

 facie elements of stability;" this definition of course distin- 

 guishes the more constant forms of varieties from the mere 

 chance aberrations w^e may meet with, but Dr. Staudinger 

 goes farther than this, and divides them into grades ; his 

 first step is what he terms " a Darwinian species," — this is 

 where the examination of a great number of specimens of 

 two forms has not enabled him to decide wdth certaint}^ 

 whether they are two distinct species or only varieties of 

 one ; a familiar example is given by the two EupithecicB, — 

 Eup. j)ulchellata and Eiip. linariata. 



The next stage is the " variety;" this is, in other words, a 

 geographical or local race. Dr. Staudinger says truly of 

 these, it is of no use arguing w^hether they are species or 

 not; this Avould vary Avitli the definition of the word, and the 

 ideas of the individual; but he adds, that it is evident that 

 they may become independent species, and curiously in some 

 places they seem to have done so, w^hilst they remain varieties 

 only in others. Lyccena Ai^taxerxes is in this sense a variety 

 of Medon, or rather Astrarche ; Ccenonyynp/ia Satyrion a 

 var. of C. Arcania. 



The third grade is the " aberration ; " and here Dr. Stau- 

 dinger evidently feels the w^ant of a fourth term and apologizes 

 for its absence. Aberrations he defines as those forms which 

 are met with at the same time, and in the same localities, as 

 the ordinary type; but then he adds, that some of these are 



