8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



suggested by the fact that "both Kleinenberg (1886) and Meyer 

 (1901) have shown that the gangha of the hind-brain are marked 

 oflf from the gangha of the nuchal organ and incorporated in the 

 brain" (Gustafson, 1930, p. 339). The same writer supposes that it 

 will be the same in other polychaets. 



The mid-brain. The most primitive form of mid-brain seems to 

 be exhibited by Eunice, where its extension in a plane and its strong 

 suggestion of segmentation into three successive and well-defined 

 divisions, which can be called mid-brain III, II, and I, can be regarded 

 in that light. Hanstrom (1927, p. 592; 1928, pp. 259, 260), it is 

 true, is very dogmatic in his expression of the opposite view ; but the 

 facts are against him. The anterior and largest pair, mid-brain III, 

 innervate the anterolateral antennae ("palps" of authors), and receive 

 the dorsal branch of the perioesophageal connectives. The middle 

 pair, mid-brain II, innervate the posterolateral antennae and the eyes. 

 The posterior and much the smallest pair, mid-brain I, innervate the 

 median antenna, which, contrary to the view of Binard and Jeener, 

 is best regarded as a coalescence of two ; when two pairs of eyes are 

 present, as in some eunicids, the posterior smaller pair may with 

 confidence be assigned to this brain division. 



In the other primitive brains, those of Euphrosyne and of Amphi- 

 nomidae the mid-brain is still extended in a plane, and its parts have 

 the same topographical relations to one another, but the subdivision 

 into three pairs is not immediately apparent. The identity, however, 

 of the succession of nerves with similar topographical relations 

 strongly suggests a composition of the same three divisions III, II, 

 and I. 



The antennae compare so closely in Eunice with the pair of tentac- 

 ular cirri on the second body segment and with the dorsal cirri on 

 the other body segments, as is the case also in the Amphinomidae 

 and in many other families, that it is quite natural to homologize 

 them. The eyes again associated with mid-brain II and I can be 

 regarded with great probability as serially homologous with the pig- 

 ment spots on the body segments of Eunice. 



From the comparisons below instituted with the visceral nervous 

 system, the writer believes that the three divisions of the mid-brain 

 represent three segmental body ganglia which have been added to the 

 fore-brain at three different times — I, the posterior, first; III, the 

 anterior, last — and that they do not belong to adjoining segments of 

 the ancestor. 



The supposed origin of these parts by the secondary subdivision 

 of a unit brain — Hanstrom's "fore-brain," consisting of our mid- 



