2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



The Amphinomorpha also are primitive ; especially (as is generally 

 supposed) in their tetraneury, in their brain (except for the hind- 

 brain), in the absence of specialization in the buccal segments, and 

 in the small protrusibility of the pharynx. But they seem less primi- 

 tive than Eunicimorpha : in their brain, both by its greater concen- 

 tration and the enormous development of the "hind" or nuchal brain ; 

 and in their stomodeum, both by its cylindrical form and greater 

 protrusibility. 



The great antiquity of the Eunicimorpha is indicated by the annelid 

 jaws (scolecodonts) which have long been known. They are abundant 

 in Paleozoic rocks; and great numbers of species have recently been 

 described, especially by E. R. Eller, from various horizons between 

 the Middle Ordovician and the Upper Devonian. Practically all those 

 described up to the present belong to the Eunicimorpha (e.g., Eller, 

 1945). Sometimes the denticles of both the "upper" and "lower" 

 jaw series are found in their natural association (Lange, 1947). The 

 claims made in this paper, however, give them a very much greater 

 antiquity than the Ordovician. 



Indications of evolution are best seen in these most primitive 

 forms; but all the errant forms furnish evidence in varying degrees. 

 The specialized "sedentary" families are naturally less satisfactory 

 for this study and need not be considered, but their ancestors doubt- 

 less experienced the same evolution. 



For the presentation of the theories given below, it is not necessary 

 to discuss the origin of segmentation. The evolution pictured fol- 

 lowed the acquirement of segmentation, and points back to a ringed 

 worm more primitive than any now existing. Moreover, it preceded 

 the acquirement of the trochophore larval stage. 



The brain with its complement of sense organs and appendages, 

 the stomodeum, and the visceral nervous system are all markedly 

 compound in errant polychaets; and it is the chief purpose of this 

 paper to claim that their structures are connected in origin. 



THE BRAIN OF EUNICE 



The brain by its form, especially in Eunice, suggests an origin in 

 a complex and lengthy aggregation. Hatschek, 1891, and Racovitza, 

 1894, were the first to divide the brain into fore-brain, mid-brain, 

 and hind-brain. lieider (1925, figs. 7, 12, 13, 15, 16) does the same; 

 and he determined minutely the external features of the neuropil 

 mass (see figs, i, 3, 4, and 5, p. 6). 



These three "brains" are here claimed to constitute three distinct 

 categories of nervous matter. 



