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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 97 



Fig 19. — Examples of generalized structure in the annelid nervous system, 

 and the structure of the annelid eye. 



A, the "rope-ladder" type of nervous system in an oligochaete, Acolosoma 

 tenebrarnm (from Brace, 1901). B, same in an archiannelid, Dinophilus conk- 

 lini Nelson (from Nelson, 1907). C, cross-section of ventral body wall of 

 Aeolosoma tcnebrarmn, showing nerve cords not separated from epidermis (from 

 Brace, 1901 ) . D, vertical section of an eye of primitive structure in a chaetopterid, 

 Ranzania sagittaria Claparede (from Hesse, 1899). E, diagram of a typical 

 annelid retinal cell (based on Pflugfelder, 1932). F, cross-section of optic rods 

 of retina of Heteroyicrcis sp. (from Pflugfelder, 1932). G, vertical section of 

 eye of a nereid, Lycastis sp. (from Pflugfelder, 1932). 



a, outer layer of epidermis over eye ; b, inner layer of epidermis forming 

 ocular vesicle (see fig. 28 C, D, E) ; Br, brain; c, optic rod of sensory retinal 

 cell ; CB, crystalline body ; Com, nerve commissure ; Cor, cornea ; Ct, cuticula ; 

 d, cell body of sensory retinal cell ; e, striated border of retinal optic rod ; Epd, 

 epidermis ; Lji, lens ; Mtli, mouth ; nf, nerve fiber ; nfbl, neurofibrillae ; Nu, 

 nucleus; Nv, nerve trunk; Ret, retina (including sensory and supporting cells) ; 

 StCovi, stomodaeal connective; VNC, ventral nerve cord. 



