514 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



ing the genitalia of dried specimens. The twentieth centuiy has produced several 

 fine taxonomic works on the stoneflies of various countries. Needham and Claas- 

 sen in 1925 presented a monograph of the North American species, and this was 

 followed by a volume on the nymphs by Claassen in 1931. In a series of fine 

 publications Th. H. Frison added greatly to these dicussions. Similar studies 

 have been published by Hynes and Kimmins in England, Despax in France, 

 Aubert in Switzerland, Kiihtreiber in Tyrol, Brinck in Scandinavia, Kohno, 

 Okamoto, and Ueno in Japan, Wu in China, Tillyard in Australia and New Zea- 

 land, and Barnard in South Africa. 



Ecological studies began with an investigation of the nymphs and the record- 

 ing of flight periods and other periodicities of the imagines. E. Schoenemund in 

 the 1910's and 1920 s laid the foundation for ecological studies but, little fol- 

 lowed until H. B. N. Hynes's and P. Brinck 's monographs (1941 and 1949 

 respectively). 



A milestone in plecopterology was the publication in 1940 of the Catalogue 

 of the Plecoptera of the World, by P. W. Claassen. It contains a bibliography, 

 which has been brought up to date by a "First Supplement," edited by J. F. 

 Hanson and J. Aubert in 1952. 



In the future there is very much to be done among the stoneflies. Primary 

 taxonomy on a critical basis is needed from many parts of the world. Mono- 

 graphs of genera and even higher categories are much to be desired. AVe know 

 about 1400 species and 138 genera; but of these about 300 species and at least 

 30 genera are doubtful. This is to a considerable extent due to the work of R. L. 

 Navas who, in many publications, presented numerous descriptions differing 

 little from those produced by most of the authors of the eighteenth century. 



Further, the present classification cannot be considered settled. W. E. Kick- 

 er's Stoneflies of Southivestern British Columbia (1943) and his Evolutionary 

 Trends in Plecoptera (1950) are fine works but what is needed is comparative 

 morphological investigations like the excellent study of J. F. Hanson on the 

 Capniidae (1946). The incongruity between the knowledge of the two best 

 known faunas, the North American and the European, is marked as regards 

 certain families and genera. 



Anatomy, histology, and physiology are very little worked fields. There is 

 a classic paper in C. F. \Vu's volume on the structure and behavior of Nemoura 

 (1923) but other works of this type have not followed. Ecology is a virgin field 

 in many respects, and should be particularly profitable in North America, with 

 its highly varied plecopteran fauna w^hich is one of the richest in the world. 

 Zoogeography is a fascinating subject in this group, of which certain genera 

 have changed very little since the Permian period and still occupy almost the 

 same regions. The geographical grouping of genera and species and their rela- 

 tionship will be very important in deciding the origin and development of the 

 freshwater faunas. 



Briefly, the stoneflies promise many exciting discoveries to present and fu- 

 ture students — but at this time taxonomy remains a formidable obstacle to 

 progress. 



