Vol. LI. LONDON, JUNE and JULY. 1919. No. 6 



POPULAR AND PRACTICAL ENTOMOLOGY. 

 The Variation of Insects, 

 by t. d. a. cockerell, boulder, colorado. 

 Nearly thirty years ago English entomologists began to take a new interest 

 in the variation of Lepidoptera, and in the interval since that time, principally 

 owing to the activities of J. W. Tutt, a very large amount of detailed informa- 

 tion has accumulated. Tutt's "British Noctuae and Their Varieties," in four 

 volumes (1891-1892), deserves to rank as a classic, although at the time of its 

 publication it was received by many with something less than enthusiasm. 

 More recently, the great monograph of the British Lepidoptera, left unfinished 

 owing to Tutt's untimely death, covered the subject of variation in an exhaustive 

 manner, including all phases of the species treated, whether British or foreign. 

 In its exhaustive character, this work runs parallel with Taylor's Monograph of 

 the Land and Fresh-water Mollusca of the British Islands, still in course of 

 publication. The variation of Lepidoptera also receives very full treatment 

 in "The Macrolepidoptera of the World." edited by Dr. Adalbert Seitz, and 

 published in English, French and German. This series of volumes, although 

 planned and published in Germany, is thoroughly international in its character, 

 a large part being written by English entomologists. The volume on the 

 Palsearctic Noctuida^, for example, is the work of W. Warren. During the 

 war publication has ceiased, and I do not know Avhether it will be continued. 



To those who had been concerned primarily with the study of genera and 

 species, all this minute attention to variation seemed rather like counting pebbles 

 on the beach. Let us assume, they said, that all species are variable, and state 

 the facts in general terms. It may be well enough to record varieties, but why 

 give them names? Will not the whole subject be buried in a complex nomen- 

 clature? It is, of course, quite true that when one is dealing with a large and 

 little known fauna, the species problem is sufficient to tax one's energies; and, 

 as a rule, the material at hand is not adequate for a study of variation. It is 

 only when the species are fair!\- well known, and large series of specimens have 

 accumulated, that such methods as these of Tutt become possible or advisable. 

 When, however, the time has come for intensive study, it must be insisted that 

 the records should l)e exact, and that all looseness of expression should be avoided 

 as far as possible. It is found, in practice, that the only way to avoid ambiguity 

 is to name and define the principal forms, which then become standards for 

 comparison. The literature is full of statements concerning "melanic" or 

 "albinic" or otherwise modified forms, which are so ambiguously referred to 

 that it is impossible to be sure what was intended. Moreover, the adequate 

 taxonomic treatment of the subject gives us a summary of what is known, properly 

 arranged and made intelligible. 



While the descriptive side of the stud>' of variation has occupied the at- 

 tention of many workers, others have taken up the subject for the experimental 



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