Taxon:5 



and it may be either sex. Some authors also designate an Allotype which 

 is a specimen of the opposite sux from the holotype. In addition, it is 

 customary and desirable to designate Prra types at the time of the origi- 

 nal description. If possible, the paratypes should be from the same 

 host, locality, etc., as the holotype. In each instance, these types 

 should carry with them precise information on locality, date, host, and 

 collector. This information sho\ild also be included in the published 

 description because of its value if the types are destroyed. In the 

 case of the holotype, it should be the only specimen on the slide. I 

 wo-uld also recommend this for the paratypes. Instances are known where 

 two specimens were on a type slide, and the author, thinking they were 

 the same species, based his description on both specimens. A subsequent 

 worker, finding that these specimens represent two species, must select 

 one of them as representing the species described by the previous worker. 

 His selection may or may not agree with the opinions of other workers, 

 and this can cause considerable confusion. I would advise all nematode 

 taxonomists to conform to the Zoological Rules of Nomenclature in all 

 taxonomic procedures. These rules are available in their original form. 

 and there are also several text books where the rules are discussed in 

 Biitiple language. 



When we place several species in one genus, we assvme that these species 

 are more closely related to each other than they are to species in 

 another genus. This same pattern applies in the groups above the genus. 

 It is one of the functions of taxonorry to attempt to show phylogenetic 

 relationships and contribute to an understanding of evolution in addition 

 to providing a means of separating and identifying populations. The 

 generic concept is entirely subjective, and we only hope that we can 

 show proper relationships by grouping species. It is natural to ask 

 what characters are usually considered to be generic. I am not certain 

 that there is any satisfactory ansvjer to this question. There are some 

 examples that can be cited, and once again it will be obvious that the 

 opinion of the individual specializing in the group is of extreme impor- 

 tance. 



The genus Trichodorus can be used to illustrate at least two points. 

 The presence or absence of caudal alae in the male is in most groups 

 regarded as being of at least a generic character. However, in Tricho - 

 dorus we presently have males with a caudal alae in some species and 

 without caudal alae in others. I must admit that there was considerable 

 temptation to make two genera of the present genus. However, I could 

 find no characters that would enable a generic separation based upon 

 females and so discarded the idea. Subsequent workers may not agree 

 iri.th this and may base such a separation upon male characters. It would, 

 however, mean that several of the species could not be placed because 

 males are not yet known. 



The number of ovaries is used as a generic character in some groups, but 

 this may be prim.arily because both one and two ovaried species are not 

 yet known. VJhen one considers that two opposed ovaries is regarded as 

 the primitive condition and that species with one ovary probably had 

 ancestors with two ovaries, as is indicated by the presence of rudiments 



