Taxon:2 



expressed by the species concept in zoology. There is sometimes a 

 tendency to regard the subspecies as being equal to the species. For 

 exanple, in the genus Meloidogyne there are a number of described sub- 

 species, and if one examines the literature it will be noted that 

 various authors have used the -names M. incognita (Kofoid and White, 

 1919) and M. incognita acrita Chitwood, 19^9, as though they were deal- 

 ing with a species and a subspecies. Properly used, M. incognita is 

 the species and there are two subspecies, M. incognita incognita and 

 M. incognita acrita . To be precise, one should indicate the subspecies 

 with which he is dealing, because the use of the species name alone 

 indicates that one or both subspecies were present. 



The present day species concept has been developed over a rather long 

 period of time by scientists working in well known groups, e.g. insects, 

 birds, mammals, etc. It is generally conceded by most workers in tax- 

 onomy that the first stage in achieving a satisfactory classification 

 is one concerned almost exclusively with the description of new species. 

 Descriptions in the less well known groups, such as nematodes, are based 

 almost exclusively upon morphology. In some respects it can be consid- 

 ered that a purely morphological classification is based, to a large 

 extent, upon gaps between species. As these gaps are gradually filled 

 in by the description of new species in a group, there should be a trend 

 toward using other biological evidence to support the taxonon^r based 

 upon morphology. Eventually, as the process of classification is con- 

 tinued, it should be anticipated that genetics, ecology, and physiology 

 will be needed to insure that a system of classification is sound. If 

 we can base our assumptions concerning taxonomy upon the trends that 

 have taken place in a group such as birds, where more than 98^ of the 

 existing species are believed to have been described, we can draw some 

 conclusions concerning the future of nematode taxonomy. 



We are certainly in the first stage of taxonomy where we are primarily 

 concerned with the descriptions of new species. Eventually, we should 

 reach a point where it will become obvious that there are more species' 

 names in the literature that there are valid species in nature. This 

 should result in extensive revisions of genera in which more use will 

 be made of the subspecies. This is the trend in well known groups, and 

 we have no reason to assume that such will not be the case with the 

 nematodes. On this basis, we can then assume that at least some of the 

 present day described species will prove to be subspecies. These sub- 

 species will be forms of a polytypic species. 



Polytypic Species - Let us take as an example the genus Trichodorus and 



consider the species californicus , obscurus , and 

 proximus j each of these species is know from widely separated geographi- 

 cal areas, and they were described from relatively few specimens in each 

 case. The descriptions are entirely based upon morphological characters; 

 that is, the gaps between these species appeared to me to be sufficient 

 to support the opinion that they were indeed new species. We will now 

 suppose that intensive collecting in areas where these species are not 

 known at present reveals forms that are intermediate and the original 

 gaps between species become occupied by forms that have intermediate 



