I'KOCEKDINGS OF UNITED STATES NATIONAL MUSEUM. 287 



to I'epiodiue here the accessible material, and wait for more information 

 before eousitleriu<;' the subject as fully decided. 



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

 cicularis, may be supposed to present the general features of the nervous 

 system in the higher members of the group. 



The accompany ing figure (C^) of part of the nervous system of Ohiton 



Tt atcVvj d. ex mow 

 cvTveTeu s 



Fig. C. — Pi^C-, pedo-biauchiaKouimissuie; A'S, uervi braucMalcs ; iV'^P, nervi pedales ; 

 h1, nervi labiales, small filaments numerous and hardly traceable; ns, nervi pharyng, 

 superiores; gpr, ganglia pedo-visceralia seu podo-braucbialia ; ifipo, inter-anterio- 

 pharyng. commissure ; ippr, inter-pedo-pbaryugial commissure ; Ajyp, anterior inferior 

 pharyngial ganglia; aipc, anterior inferior pbaryugial commissure; j^Wf^j posterior 

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

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

 superior pharj'ngial ganglia ; Pxp, posterior superior pharyngial ganglia ; x, superior 

 posterior post-pharyngiaU a ngliou; ~, anterior superior pharyngial commissure ; Isp, 

 inter superior pharyngial commissure; oo, anterior inferior pharyngial nerves; jy), 

 posterior ditto. 



termini as -nell 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 api>ly this reasoning to the matt^^r in hand in detail would require much more 

 space and lime than arc at present available. Yet it may bo 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 featirres from the ten- 

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

 very small number of segments, while the worms are characterized I'ather by redupli- 

 cation of UKU'c simple segmental part sin great number, but small variety among them- 

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



