THE NEW GENEALOGICAL TR£E 415 



(Tardigrada, Pentastomida, and Onychophora) do not "de- 

 serve" to be given the category of subphyla. All these three 

 groups can be considered as very specialized Arthropoda. 

 Beklemischew has also given the rank of an independent sub- 

 phylum to the Sipunculoidea (he calls them Prosopygia) as well 

 as to the Kampto2oa. He places these two subphyla after the 

 Arthropoda which is certainly quite unusual. In this connection 

 we can also dispense well enough with the category of super- 

 classes even if it is true that among the classes of the Polymeria 

 there are some groups which are phylogenetically more closely 

 related, similarly as has been the case with the Ameria. 

 It seems that w^e will probably come to a generally acceptable 

 scheme of the system of the Polymeria if we abandon these 

 unnecessary subdivisions. 



The subphylum AnneUda can be well enough subdivided 

 into three classes, the Polychaeta, CHtellata, and the Echiuro- 

 idea. The class Polychaeta is the main one w^hose ancestors 

 had evolved into all the other subtypes as well as into the 

 Arthropoda and into the next phylum Oligomeria. Several 

 zoologists have given the rank of a class to the group Myzo- 

 stomida; I myself have done this in my proposed genealogical 

 tree of the anim^al world (Hadzi, 1944:179); this, h wever, is 

 really not necessary. The Myzostomida can be considered as 

 specialized Annelida of the type of the Polychaeta; this is also 

 the way how they are treated in the system proposed by 

 Beklemischew. It is almost a question of personal taste whether 

 we unite the Oligochaeta and the Hirudinea, the two groups 

 of the Annelida, into a new group CHtellata, or whether we 

 consider each of them as an independent class. There is no 

 disagreement among zoologists that the Arthropoda evolved 

 from some AnneUda-like ancestors. Yet we are still uncertain 

 about the way along which this evolution had proceeded, 

 whether the Arthropoda evolved once only or after repeated 

 similar attempts made by Nature. The systematists of the 

 Arthropoda show in this point a considerable variety of 

 opinions. For the present we can again avoid the obligatory 



