THE NEW GENEALOGICAL TREE 399 



far we are still unable to present a strict proof which would 

 definitely support the one or the other thesis. We cannot 

 completely exclude the possibility that the perigastrocoele did 

 not evolve once only; yet as much as wc know and think now 

 about the emergence of new types, this possibility does not 

 seem to be very likely. The standpoint we take again depends 

 heavily on the way we interpret the various phenomena that 

 can be observed during the ontogenies. The interpretation 

 of ontogenetic morphogeny has had a decisive influence 

 on the way scholars have tried to solve the problem of the 

 perigastrocoele and of its segmentation. The transition from 

 the not-segmented to the segmented state must necessarily 

 be recapitulated somehow^ in the ontogenies, yet this can be 

 either a recapitulation of the ontogenetic development that 

 had taken place during the phyletic past of an ontogeny, or 

 it is partly a recapitulation of states that had existed in the 

 adult (functioning) ancestors. 



If now we first take a look at the conditions that exist in 

 the adult recent Ameria we find that here there are no genuine 

 transitory forms. This could actually be expected. Those forms 

 that could eventually be interpreted as transitory forms be- 

 tween the state with a uniform perigastrocoele and that with 

 a more or less segmented perigastrocoele give an 

 impression of a secondary retrogression, of an oligomery 

 combined with a change in the way of Hfe or with a change 

 in the type of movement (to a burrowing or semi-sessile way 

 of life). Later we will again return to this same problem. 



Among the recent Ameria, the Nemertinea are "the" group 

 in whose organization we can find the greatest concentration 

 of those elements that had probably led to the emergence 

 of the type Polymeria. The Nemertinea show a strong inclina- 

 tion through their increased length combined with a sinuous 

 type of movement, to a formation of various kinds of coeloms 

 (the rhynchocoele, the gonocoele combined with the gono- 

 choristic state and with a simplification of the auxiliary organs, 

 the haemocoele, and the nephrocoele), to a development of 



