THE NEW GENEALOGICAL TREE 437 



supports my thesis of an evolution of the Sipunculida from 

 the ancient Annelida. It does in no way corroborate the 

 opposite thesis which was formulated, for example, by 

 Hyman (1959, Vol. V., 690) with the following words, "The 

 Sipunculida are therefore to be conceived as protostomatous 

 coelomates placed along the main line of the Protostomia that 

 leads to Annelida, Mollusca, and Arthropoda." 



The Oligomeria as the Initial Form for the 

 Evolution of the Chordonia 



One of the characteristics of the Oligomeria is the fact 

 that they do not include even a single subgroup (class) whose 

 species would lead a life considered as characteristic of the 

 Eumetazoa. There is one class only which includes exclusively 

 freely moving species (the partly inert Spadella does not 

 disturb this general picture); these are the Chaetognatha. We 

 have already stated at the beginning of the present study 

 that life in free water cannot be considered as a primary and 

 normal way of life. I have tried to solve the problem of 

 the Chaetognatha together with Lameere by attempting to 

 derive them by way of neoteny from the planktonic larvae 

 of the Brachiopoda. This type of derivation corresponds best 

 with the known facts. The Chaetognatha, as strongly specialized 

 Oligomeria, cannot be taken into consideration as a possible 

 initial form for the evolution of the Chordonia. The similari- 

 ties that can be observed between the Chaetognatha and some 

 small fishes are a purely external phenomenon. The structures, 

 the ontogenies, and the types of movement, however, are 

 entirely different in these two animal groups. 



Free mobility has been attained secondarily by the 

 Oligomeria in two other instances. We find, however, that 

 in spite of a prolonged evolution the Echinodermata have 

 still preserved traces of an original radial symmetry that evolv- 

 ed from an even older bilateral symmetry. This can be seen 

 29 



