NO. 6 



CLASSIFICATION OF NEMATODES — FILIPJEV 



The first question arising in any attempt at nemic taxonomy is 

 the general relation of the free-living and parasitic forms. Until re- 

 cently there have been expressed in the literature opinions to the 

 effect that the Nematoda are chiefly parasitic, a small part of them 

 being free-living, mostly living in decaying substances. That point 

 of view is completely wrong and is, of course, merely a result of the 

 historical sequence in the study of this group, because in its early 

 development much more attention was paid to the larger and eco- 

 nomically more important parasites than to the inconspicuous and 

 apparently economically unimportant free-living forms. 



The comparison of the number of described species in both 

 groups is somewhat suggestive. The very approximate number of 

 species described up to the end of 1930 is as follows : 



Free-living, 2,165; parasitic, 2,436. 



These figures must be regarded as subject to considerable correc- 

 tion, as it is probable that a much larger number of parasites than of 

 free-living forms are known to science. Systematic studies of the 

 former were begun more than a century ago by Rudolphi in 1819, 

 and since then hundreds of workers have been engaged in a study of 

 them. The study of free-living forms began with Bastian in 1865, 

 almost 50 years later; and it is only in the last 15 years that there has 

 been a notable increase in number of workers, making a total today 

 of about 15 workers engaged in the study of them, which is, of 

 course, a decided gain when compared with two or three working 

 along this line at any one time before about 1912. 



