. Bulletin. Natural history; Natural history. September F'i? ROSS: NEARCTIC ALDER FLIES 59 Preservation and Preparation of Material The most satisfactory method of pre- serving specimens seems to be in fluid. We have used 80 per cent ethyl alcohol witii good results. Genitalia and other diag- nostic parts of specimens so preserved usually may be seen without injuring the specimen or performing other preparation. If a specimen is pinned, its abdomen must usually be removed and cleared before it is possible to give a complete diagnosis. The follow technic has been used with fine results: soak th
. Bulletin. Natural history; Natural history. September F'i? ROSS: NEARCTIC ALDER FLIES 59 Preservation and Preparation of Material The most satisfactory method of pre- serving specimens seems to be in fluid. We have used 80 per cent ethyl alcohol witii good results. Genitalia and other diag- nostic parts of specimens so preserved usually may be seen without injuring the specimen or performing other preparation. If a specimen is pinned, its abdomen must usually be removed and cleared before it is possible to give a complete diagnosis. The follow technic has been used with fine results: soak the abdomen for three to six hours in cold 10 per cent caustic potash (KOH) solution, change to distilled water for an hour or more, then with for- ceps and needle gently press out the dis- solved viscera. This leaves a fairly trans- parent shell which may be preserved and studied in 80 per cent alcohol or glycerin. Illustrations The illustrations of genitalia used in this paper are made from specimens treated in caustic potash solution. They are drawn with the parts considerably expanded, since it is only in such a position that some details can be seen clearly. Value of Characters Genitalia have provided the best char- acters for separation of species, although other characters may be of value. Differ- ences in wing venation are subject to considerable individual variation and ma\ be expressed at best as averages and not as absolute characters. For example. (/ilifornica usually has three or four branches of R,, but may have only two, whereas velata and some others usualh have only two branches of R2 but ma\' have three or four. The cross-veins of the costal area of the front wing vary in the same fashion: americana has four to six, nioliri has four to 10, averaging seven, and the others have 10 to 15, averaging 12 or more. Differences in punctuation and gloss of the head are quite constant, but offer no differences between many species. It is difficult to express some of these
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Keywords: ., booka, bookcentury1900, bookdecade1910, booksubjectnaturalhistory
