THE ORDERS AND CLASSES OF NEMAS* , 



CONTRIBUTIONS TO A SCIENCE OF NEMATOLOGY, VIII 

 BY N. A. COBB 



Our first adequate conception of the nema phylum will come from 

 a study of the free-living forms, for in parasitic nemas it frequently 

 happens that the structure of important organs, especially those of the 

 mouth and alimentary canal, is greatly simplified through degenera- 

 tion. This degeneration proves to be relatively as marked among the 

 parasitic nemas as it is among parasitic species in other phyla con- 

 taining both free-living and parasitic forms, so that from the standpoint 

 of comparative morphology, they are often very highly perplexing. 

 On the other hand, it is already possible, through comparative study 

 of the known free-living genera, to begin formulating some of the prin- 

 cipal features of the orders and classes of nemas and to do it with suffi- 

 cient truth and clarity to make the results useful to investigators, 

 teachers and students. 



The following table outlines a classification of the phylum, based 

 on a study of several hundred genera. It is a comprehensive classi- 

 fication I have long employed, that has proved useful in many ways. 

 It sets forth relationships based on and correlated with the mouth- 

 parts. In most animal phyla where there is a distinct mouth, oesoph- 

 agus and stomach, experience has amply proved the utility of these 

 portions of the anatomy as a guide to phylogenetic relationships. 

 While some parts of the following scheme appear to outline clearly and 

 permanently certain fundamental truths, other parts undoubtedly will 

 have to be expanded or altered,f since our knowledge of details is still 

 inadequate to a clear view of all the larger relationships. 



In the table, the order columns are staggered, in an attempt to 

 indicate relative importance, the farther to the left the words, the 

 more comprehensive or significant is the meaning to be attached to 

 the corresponding order name. 



* Waverly Press, July 19, 1919. 



t Perhaps it may not be going too far to suggest that, in any such expansion and alteration, the aim 

 be, among other things, to make the terminology of the phylum both euphonious and characteristic. 

 Too few appear to realize how important it is that such a terminology be (1) As descriptive and as nearly 

 self-explanatory as possible. (2) Few, short and consistent in its roots. (3) Simple and brief in its 

 terms. (4) Characteristic and euphonious. (5) Such as lends itself readily to modern inflections and 

 derivations. 



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