THE CLASSIFICATION OF THE FREE-LIVING 



NEMATODES AND THEIR RELATION 



TO THE PARASITIC NEMATODES 



By I. N. FILIPJEV, 



Leningrad, USS.R.; Seessel Research Fellow, Yale University ig28-2g 



(With Eight Plates) 



There are several opinions as to the position of the Nematoda 

 in the animal kingdom. Cobb (1920) suggests that they constitute 

 an independent phylum. There is much in favor of that point of 

 view, as the Nematoda do not have very near relatives among other 

 animal forms. However, in dealing with forms of such low organi- 

 zation as the nematodes, we must consider not only the purely 

 morphological peculiarities, but the general structure and embryolog}' 

 as well. A consideration of these things shows that there are some 

 related forms, perhaps not so very closely related, but with the same 

 chitinous cuticle and bilateral determinative type of cleavage. The 

 group received its definition, as well as its name, from Grobben, 

 who called it Aschelminthes and included in it the Rotatoria, 

 Gastrotricha, Echinoderida, Nematoda, Gordiacea, and Acantho- 

 cephala. Besides the above-mentioned embryological resemblance, 

 all of these have the following common features : A functional 

 primary body cavity, absence of a circulatory blood system, an anal 

 opening if there is an intestine, a more or less cylindrical form of 

 body with a circular cross-section, and a firm external cuticula. The 

 recognition of this group is very convenient and as yet is not con- 

 trary to our knowledge of these forms, although not all of its mem- 

 bers show unquestioned relationships (cf. Brandes). 



The last three groups are often treated together as a phylum or 

 class, the Nemathelminthes. This does not seem to be an entirely 

 satisfactory point of view, especially as regards the Acanthocephala, 

 which are compared by Cholodkovsky to the Platodes, although re- 

 cently Meyer has found that the type of cleavage is the same as in 

 the Rotatoria. The Gordiacea, although showing a greater re- 

 semblance, are, of course, not directly connected with the Nematoda 

 (Vejdovsky). Heider's discussion also seems to permit of recog- 

 nizing a systematic relationship among these groups. 



Smithsonian Miscellaneous Collections. Vol. 89, No. 6 



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