2 MEMOIRS ON THE COLEOPTERA 



a retinue of subordinate forms, given various designations, such as 

 subspecies, varieties and aberrations, the very convenient binomial 

 nomenclature of Linne stands in grave danger of destruction. It 

 should be added, furthermore, that when the species is made thus 

 composite there is no definite limitation to the forms that may be 

 included under a single specific name, giving rise to purely arbitrary 

 and more or less inharmonious aggregates of greater or less extent 

 according to personal whim or fancy. It would be far better and 

 more in concordance with reality, to limit the word species to those 

 forms which constantly exhibit the same peculiarities of structure 

 and habitus, and which do not produce fertile hybrids with related 

 forms, or, in the present state of knowledge, which appear to be in- 

 capable of so interbreeding. For example, in the genus Omus 

 forms have been assigned subordinate rank when the male sexual 

 apparatus is so constituted as in all probability to prevent even the 

 act of copulation, and, if this be the case, there could be no better 

 proof of complete specific isolation. 



After an experience of a third of a century in collecting large 

 series of many species, the writer can state with complete conviction 

 that, aside from polymorphism and certain occasional accidental 

 deformities, there is, as a rule, no such structural variation among 

 the individuals of a species as is maintained by some of the present 

 schools of systematists. There is before me, for example, as I 

 write, a series of 275 specimens of Saprinus lugens taken in Arizona, 

 and, except in size and a slight spreading or retraction of the suffused 

 punctuation, there is no asexual variation that would be noticed 

 anywhere in the series. In regard to the prevailing ideas of vari- 

 ation let us take the surface sculpture in Pterostichns cristatus Duf. 

 In iridescent forms, such as Loxandrus, the iridescence is easily 

 observed to be due to a set of very close-set transverse incised lines 

 producing a diffraction grating, such as is used by physicists for 

 producing a spectral image.* A species not having this iridescence 

 has sculpture of an entirely different kind, the fine lines on the sur- 



* The most remarkable natural diffraction grating known to me is that engraved 

 upon the elytra of the Phalacrid genus Litolibrus Shp. All the species have remarkably 

 strong opalescence and the brilliant spot on the hemispherical elytra of obesus is a 

 pure and perfect though short spectrum, with all the colors evident from red to violet. 

 This grating is entirely unresolvable under a three-fourths inch objective and the parallel 

 lines are probably fully as fine and close as in the celebrated Rowland diffraction grating. 



