THE NEW GENEALOGICAL TREE 417 



cannot propose any new ideas here which would clarify these 

 points. The Arthropoda probably evolved on the sea bottom 

 and along several radiating lines. The hypothesis proposed by 

 Giljarov about the origin of the youngest (and in spite of this 

 very old) group Hexapoda from some ancestors similar to the 

 Myriapoda wich had lived in the soil seems to me to be very 

 probable. The Arthropoda left the sea several times to live 

 on land; and this is also true for the Polymeria as a whole. 



The number of subtypes is smaller in the Polymeria if we 

 compare them with the situation which can be found in the 

 Ameria. There, in one subclass only, which consists entirely of 

 species that live as parasites, are the Pentastomida 

 among the Chelicerata; on the other hand we find among the 

 Ameria three classes which consist exclusively of the parasitic 

 species. At the same time, however, we can identify parasitic 

 species or even whole subgroups in other classes of the Arth- 

 ropoda also (with the exception of the Onychophora and the 

 Myriapoda). Among the Cirripedia we can find endoparasites 

 whose form had been simplified beyond recognition so that it 

 is their freely swimming larva only which shows their arthro- 

 podal provenance. 



Among the Polymeria we cannot identify a single class of 

 fully sessile species while on the other hand there exist two 

 such classes among the Ameria (Cnidaria, Endoprocta). The 

 reason for this is the fact that a fully sessile way of life can 

 exist in a fluid medium only because a majority of the Poly- 

 meria are now terrestrial animals. There is one group only 

 among the sea, inhabiting Polymeria (the Cirripedia among the 

 Entomostraca) which includes fully sessile species; yet again 

 these Cirripedia do not form any colonies (cormi) because they 

 have completely lost the ability to reproduce asexually. It is 

 noteworthy that forms similar to cormi have been developed 

 by the Polychaeta which reproduce by way of division and of 

 budding. 



There is, however, another point which we find most in- 

 teresting in connection with the way of life of the Annelida 



