THE NEW GENEALOGICAL TREE 423 



level afterwards. Due to various specializations this new type 

 again evolved into various subtypes. Here we can find only a 

 few side lines that led to a simplification of the organization 

 because of a retrogressive trend in their evolutions (Tardi- 

 grada, Pentastomida among the Chelicerata, Acarina, the 

 parasitic Cirripeda; among these there may also be some cases 

 of neoteny). Several classes and subclasses have reached a very 

 high level of organization, especially among the Arthropoda, 

 with the Insecta as the highest point of this development. Had 

 there been no further evolution, first in a retrogressive direc- 

 tion (Oligomeria) which w as followed by a progressive evolu- 

 tion (Chordoma) ; the Arthropoda with the Chelicerata and the 

 Insecta would be the two groups representing the climax and 

 the end of all the evolution of animals. 



The Sphere of the Phylum Oligomeria 



Those who believe in a dichotomy of the "Coelomata" into 

 the Protostomia and the Deuterostomia meet with great 

 difficulties as soon as they try to drav/ exact limits between 

 these tw^o main subdivisions of the Coelomata. This could not 

 be the case if these two subdivisions really stood clearly in 

 opposition to each other, as was originally believed. Above all 

 there should be no such combinations as protostomy on the 

 one hand, and enterocoely on the other, or vice versa; yet 

 such combinations do actually exist. We can avoid these and 

 many other difficult and unpleasant facts if we interpret these 

 apparently conflicting phenomena by means of the mosaic 

 theory; if we consider that both the deuterostomatous and the 

 enterocoelic states evolved from the protostomatous and 

 ecterocoelic states. For the sake of a more easy understanding 

 of these processes we will find it helpful, as this has repeatedly 

 been emphasized, if we take into consideration the changes in 

 the way of life and if we exploit more critically the ontogenetic 

 facts. 

 28* 



