NO. 8 THE POLYCHAET — RAW 33 



CONCLUSION 



Both in their complexly folded stomodeum and in their brain the 

 Eunicimorpha are claimed as the most primitive of polychaets. Their 

 study suggests the characters of the ancestral annelid and the subse- 

 quent evolution of the complexities of the stomodeum, the brain, 

 and the visceral nervous system of the polychaet. 



In brief, on this view, the ancestors of the polychaet, in connec- 

 tion with their successive modes of feeding, transferred not only the 

 external skin, but also the nerves and ganglia of the central nervous 

 system, which at that time were lateral in position, and also the 

 appendages associated with those ganglia, up the alimentary tract 

 in the formation of the stomodeum. As a primary result they have 

 originated (or greatly added to) their visceral nervous system ; and 

 as a secondary result have complicated their brain. The dominating 

 factors were the invaginations ; and the structure of the eunicid shows 

 that these took place three times over. (An analogous process took 

 place yet again in the evolution of arthropods, as the writer hopes 

 to show.) 



Most of the fundamental ideas expressed in this paper are already 

 summarized on pp. 19 to 27. 



Though the evolution here claimed is so great and so widespread, 

 it is not believed to be beyond the capacities of variation and natural 

 selection to effect. 



As a last word the author desires to thank Dr. E. G. Butler, Dr. 

 J. Percy Moore, and Dr. Ernst Mayr for their encouragement. 



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1928. Morphologic du lobe preoral des Polychetes. Recueil Inst. Zool. 

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1923. Polychetes errantes. Faune de France, vol. 5. Paris. 



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