PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 287 



to reproduce here the accessible material, and wait for more information 

 before considering the subject as fully decided. 



The figure here given, after Brandt's researches on Acanthochiton fas- 

 ciculariSj may be supposed to present the general features of the nervous 

 system in the higher members of the group. 



The accompanying figure (C 2 ) of part of the nervous system of Chiton 



Fig. C. — PBC, pedo-branchial commissure ; XB, nervi branchiales ; XP, nervi pedales ; 

 nl, nervi labiales, small filaments numerous and hardly traceable ; ns, nervi pharyng. 

 superiores; gpv, ganglia pedo-visceralia seu pedo-branchialia ; iapc, inter-anterio- 

 pharyng. commissure ; ippc, inter-pedo-pharyngial commissure ; App, anterior inferior 

 pharyngial ganglia; aipc, anterior inferior pliaryngial commissure; pipe, posterior 

 ditto; gv, ganglia vascularia, resting on bv, a blood-vessel (the small commissure sep- 

 arating these ganglia is called by Brandt the intervascular commissure) ; sp, anterior 

 superior pharyngial ganglia ; Psp, posterior superior pharyngial ganglia ; x, superior 

 posterior post-pharyngial ganglion ; z, anterior superior pharyngial commissure; Isp, 

 inter superior pharyngial commissure; oo, anterior inferior pharyngial nerves; pp, ' 

 posterior ditto. 



termini as well as routes, with adults rather than embryos. We do not live in a world 

 of embryos alone, in any but the most metaphysical sense. We cannot learn the rela- 

 tions of animals, as they are, to each other from the embryological phylum alone, any 

 more than we could understand the nations of modern Europe and their political 

 boundaries from a map of the Aryan migrations. 



To apply this reasoning to the matter in hand in detail would require much more 

 space and time than are at present available. Yet it may be said that we have high 

 authority for considering that the mollusks and worms are derived from a common 

 origin, and that, in fact, the former derive their characteristic features from the ten- 

 dency to specialization and developement within the compass of a single segment, or a 

 very small number of segments, while the worms are characterized rather by redupli- 

 cation of more simplo segmental parts in great number, but small variety among them- 

 selves. Various groups of mollusks may owe their greater or less participation in fea- 



