502 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



is yet understood. The cytology and genetics are virtually unknown. Some of 

 the best new research on biology of the Collembola is in the substantial series of 

 papers on dynamics of soil populations and comparisons of populations in a 

 variety of environments. We may expect this area of knowledge to develop 

 rapidly. 



Protura 



Following Silvestri's discovery of the Protura in 1907 and the publication of 

 Berlese's fine monograph in 1909, perhaps sixty new species have been described. 

 Many are from North America (about 20) and Europe, but Protura have been 

 reported from most parts of the world. There are seven or eight genera vari- 

 ously placed in two or three families. The taxonomic investigations have been 

 the work chiefly of Womersley, Ewing, Conde, Strenzke, Bagnall, and Gisin. 

 Tuxen (1949) has traced the postembryonic development with great care. Other- 

 wise, regrettably little new information on the morphology, physiology, and de- 

 velopment of the Protura has been published since Berlese's early monograph. 



The most urgently needed investigation is an analysis of the embryonic de- 

 velopment comparable to those of Tiegs on Pauropus and Hanseniella. 



Entotrophi 



The Entotrophi (also variously called Diplura, Dicellura, Rhabdura, En- 

 tognatha, Aptera, etc.) being far more numerous and conspicuous to contempo- 

 rary collectors than insects in groups such as the Strepsiptera, it is surprising 

 in retrospect to find how tardily they became known. One of Linnaeus' original 

 Podura species is supposed by some entomologists to be a Campodea. However, 

 the first species recognizably in the Entotrophi is Westwoods Campodea staphy- 

 linus (1842). Not until 1864 did Haliday describe lapyx solifugus, the first 

 genus and species of the lapygidae. Some members of this family are about five 

 centimeters long, few are tiny, and they seem to occupy all regions with a mild 

 climate. Yet they went unnoticed until as late as 1864, when .an Englishman de- 

 scribed specimens he took in southern Italy. The next year Meinert named a 

 second species of Campodea, and soon the number of named species of Campo- 

 deidae and lapygidae began to increase materially. Packard described a caverni- 

 colous species of "Campodea" from Mammoth Cave in 1871, and at about this 

 time cavernicolous species were being described from Europe. 



The third major group of Entotrophi, the family Projapygidae, was discov- 

 ered in Africa by Cook and named in 1899. Silvestri presented a series of de- 

 tailed studies of the anatomy of the family during the next few years. 



Filippo Silvestri is the one man whose work stands far beyond that of any 

 other specialist on the Entotrophi. From 1898 to 1948 he wrote about ninety 

 papers on Campodeidae, lapygidae, and Projapygidae. Nearly all are devoted 

 solely to descriptions of new genera and species, and unfortunately Silvestri 

 was particularly remiss in not synthesizing his work from time to time. Only 

 once, in 1905, did he set forth his views on the full higher classification of the 

 Entotrophi and Thysanura. He almost never used keys to species after 1910. 

 Nevertheless, his descriptions and figures are usually recognizable. The number 



