524 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



Psocids were first segregated as a unit group {Psocus) in Nenroptera by La- 

 treille (1794, France). Then Leach (1815, Scotland) set up separate divisions 

 for winged and wingless forms. Although wing venation had been used for 

 grouping by Stephens (1836, England) and Burmeister (1839, Germany) 

 it had been utilized only twice — by Curtis (1837, England) and Burmeister — 

 in generic diagnoses. 



The period from 1853 to 1903 was marked by the establishment of wing vena- 

 tion as the prime factor in generic differentiation. This was accomplished mainly 

 through the influence of the pioneer studies of Hagen (1849-1886; Germany 

 until 1870, thereafter U. S.). His bibliographical research, his monographs on 

 wingless psocids and fossils in amber, as well as much descriptive work and a 

 full synonymic synopsis with terse generic diagnoses, paved the way for later 

 advances. In this country new species were described by Walsh (1862), Aaron 

 (1883-1886), Packard (1889), and Banks (1892-1901), but the contributions 

 of a wider scope were still being made by European workers, notably by Mc- 

 Lachlan (1866-1903, England) and Kolbe (1880-1888, Germany). The latter, 

 a Darwinian disciple, having fancied resemblances with stages of evolutionary 

 development, proposed a classification in five sections, which failed, however, to 

 supersede Leach's simpler arrangement. Comstock (1895, U. S.) questionably 

 limited the order Corrodentia to psocids. So at the close of this fifty-year period 

 the psocids held family or superfamily rank in the order Neuroptera. About 

 one hundred fifty papers had appeared, most of them concerned with syste- 

 matics, a few with biology and general morphology. 



Two overlapping phases of nearly equal extent can be recognized in the 

 period from 1903 to 1953, during which the number of described species in- 

 creased rapidly. In the earlier phase the quality of the systematic papers con- 

 tinued at about the same level as previously, but there was an increase in their 

 quantity and in their geographic range. The firm establishment in 1903 of a 

 suborder (Copeognatha) for psocids exclusively marked the beginning of a pro- 

 lific period for Enderlein (1900-1936, Germany). Much of his work is especially 

 valuable because it consists of regional or group surveys. Particularly note- 

 worthy is his occasional use of genitalic and other characters having positive dis- 

 criminatory worth, though — ^with the exception of tarsal segmentation, which was 

 thought to mark a fundamental dichotomy — they were, for the most part, re- 

 garded as subsidiary to venation. Other outstanding writers were Banks (1903- 

 1947), Ribaga (1900-1911, Italy), and Navas (1907-1936, Spain). Shipley 

 (1904, England) raised the psocids to ordinal rank when he limited the order 

 Psocoptera to psocids exclusively. Perhaps of equal systematic importance dur- 

 ing this period was the demonstration of the unreliability of venation as a basis 

 for classification. Although this was clearly indicated by the divergent views 

 of relationship expressed in the proposed classifications of Enderlein (1903, 

 1911), Tillyard (1926, New Zealand), Banks (1929) and Karny (1930, Java) 

 the fallacy was not recognized until the second phase of this period. 



During this next phase, covering the last thirty years, with the general adop- 

 tion of alcohol as a preservation medium and the more accessible and improved 

 stereoscopic microscopes, the emphasis has centered on a search for reliable taxo- 

 nomic characters. Genitalic conformation has been found to be of special value, 

 as indicated by the studies of Chapman (1930), Gurney (1939, 1949), and Som- 



