THE NEW GENEALOGICAL TREE 



457 



ways. The small size of a group can be due to the fact that 

 it evolved by way of neoteny (this is true for the Chaetog- 

 natha, Ctenophora and the Larvacea), or it is a consequence 

 of an ageing of the line of evolution and thus an indication of 

 a decaying phase which can finally lead to a complete extinction. 



Mammalia 



(Tetrapoda) 

 Chondrichthyes 



Protichthyes ^^-.r] y 

 (Acanthodes+ /^•,Vi 

 Arthrodira) (Pisces] 



Osteichthyes 



Agnatha 



Ostraco- _^. 



dermata ^ 



Acrania 



Tunicata 



OUgomeria 

 (Enteropneusta) 



Fig. 59. Genealogical tree of the phylum; Chordonia. 



Such a case is probably represented by the Brachiopoda. The 

 small size of a group can also be a consequence of a hyper- 

 specialization, as is the case, for example, with the Pogo- 

 nophora. 



The Genealogical Tree of the Entire Animal World 



After we have constructed partial genealogical trees which 

 show^ the individual phases in the phylogeny of the animal 

 world we still have to bring them together and to construct 



