T;i7on:)i 



should iiranediately indicate to the taxonomist that there is the possi- 

 bility of the presence of the polytypic species group, ajid he should be 

 prepared to accept this possibility if he describes the geographically 

 isolated populations as species. In practice, we hope that the morpho- 

 logical differences between allopatric species are substantial; that is, 

 the gaps should be large so that there is little possibility that they 

 will be filled by intermediates. It is anticipated that in the future 

 more use will be made of ability of populations to interbreed or not to 

 interbreed as one of the criteria for the validity of a species. But, 

 as inticated earlier, the genetist, physiologist, and economic nematolo- 

 gist must contribute information to supplement the purely morphological 

 species concept that must, of necessity, be the concept most used by the 

 taxonomist of nematodes at the present time. 



When Dr. Cairns asked me to discuss taxonomy, I imanediately asked him 

 what sort of information the group would be most interested in consider- 

 ing. He suggested that we might discuss the degree of morphological 

 difference required in order to describe a new species and how to arrive 

 at a decision regarding the morphological characters used to distinguish 

 subspecies. As I have indicated previously, at least by implication, 

 the species concept is subjective. By this we mean that it is impossible 

 to see all of the individuals that comprise a species, so we must make 

 certain assumptions based upon small samples. There are no set rules or 

 criteria that are precise enough to allow us to say that morphological 

 differences of a certain magnitude must be used to separate species. In 

 actual practice, it is the opinion of the individual tajconomist that 

 determines the composition of the various categories. For this reason, 

 I consider it would be foolhardy on my part to attempt setting up cri- 

 teria to be met before a nematode could be described as a new species. 

 At the subspecies level it has been suggested that subspecies are Justi- 

 fied when it is possible to distinguish 1$% of the individuals of one 

 population from another on a morphological basis. My present opinion 

 is that our classifications must be based upon morphological characters, 

 which may or may not be associated with differences in host plant range, 

 etc. I would certainly suggest that the individual conterr^jlating 

 describing a new species should devote considerable time to the study 

 of other species in the gennc;. He should examine the group and attempt 

 to form an opinion as to the characters used by other authors in dis- 

 tinguishing the species. He should look for additional characters that 

 have not previously been used. He should finally ask for opinions of 

 others interested in the same groups. If they agree with his opinions 

 concerning the species, he should be most happy and describe the new 

 species without hesitation. If there is a difference of opinion, he 

 may proceed with the description, but possiblity only after additional 

 study. 



I believe that it would be appropriate to briefly mention types. It is 

 rncom]ncnded in the Zoological Rules of Nomencalture that when a new 

 species is described, one specimen should be designated as the type. 

 This specimen becomes the name bearer, and, so long as it is in exist- 

 ence, it represents the spccicr-. The type specimen is objective; it 

 can be seen, measured, studied, etc. This specimen is the Holotype, 



