THE NEW GENEALOGICAL TREE 419 



segments, the acron included. In several sublines we can 

 observe a parallel development towards a stabilization of the 

 number of segments, e.g. in the Crustacea where the number was 

 fixed at twenty. Yet even in these lines the oligomerization can 

 continue to have an important role, above all in the side lines 

 with a specialized way of life (e.g. the Pentastomida), or with a 

 strongly diminished size of the animal body (e.g. the Acarina). 



The part of these Polymeria which evolved progressively 

 reached its climax in several groups of the Polymeria that Hve 

 in water and on land and whose evolution has alw^ays ended 

 blindly. It should be mentioned in passing that during this 

 development the conditions of the perigastrocoele and of the 

 other coelom cavities had also been considerably changed and 

 that this development led to the formation of a secondary 

 myxocoele. Among the Arthropoda that live in the atmosphere 

 we find the "worm-like forms" still preserved in the Pro- 

 tracheata (Onychophora) and in the Myriapoda s.L, as well 

 as in the larvae of numerous insects. 



Now, we must return to the primitive Polychaeta among 

 the Annelida. A part of these had given up the mobile way of 

 life and predatory macrophagy and had begun to live as sessile 

 and microphagous anim.als. This transition was made by freely 

 moving species which had developed temporary protective 

 tubules. Such species have been preserved down to the present 

 day. The tubicolous way of life is different from the truly sessile 

 way of life where the animal becomes directly attached to the 

 substratum after metamorphosis had been completed. In this 

 line of evolution we can also find formation of regions (e.g. 

 Chaetopterns) and a diminution of the size of the body which 

 had also led to a reduction of polymery, yet no special new 

 type ever emerged as a consequence of this development. It 

 has always remained a blindly ending side branch. 



The radiating lines of evolution which started from the 

 prototype of the Polychaeta proceeded even further. A part 

 of these abandoned life on the free surface of the sea bottom 

 and penetrated partly into its soft sediments where they 



