THE ANATOMY OF SCALIBREGMA INFLATUM. 275 



the exception of Capitella), and their leLitions and 

 structure have been exhaustively investigated by Eisig 

 (1887, p. 494). B. Meyer ^ has described the small and 

 simple ''Seitenorgane" of PolyophthaJmus pictus. These 

 are, I believe, the only hitherto published accounts of the 

 lateral sense organs of Polychaetes. 



These sense organs of Scalibregma closely resemble 

 those of Capitellida3, except that in the latter there are no 

 large ganglion cells beneath the rods. I have also found 

 similar sense organs in specimens of Eunienia crassa and 

 Lipobranchius jeffreysii, whicli reached me when this 

 paper was almost completed. In the two latter genera, the 

 depression in which the sense organ is lodged is easily visible 

 on each side midway between the notopodium and neui'o- 

 podium of each chsetigerous segment. In several cases the 

 sensory papilla and the "hair field" can be clearly seen 

 within the depression. 



From an examination of published figures of Polychaeta it 

 appears probable that " Seitenorgane " are rather more 

 widely distributed than is generally supposed, for there are 

 certain structures shown in these figures which strongly 

 remind one of lateral sense organs, both by their position 

 and appearance. It was stated above (p. 270) that the aper- 

 tures of the depressions containing the sense organs of 

 Scalibregma have been mistaken by earlier observers for 

 sexual openings. It is probable that certain apertures de- 

 scribed as occurring in a corresponding position in other 

 genera may eventually be shown to be depressions lodging 

 sense organs. S. Joseph (1898, p. 371, and pi. xxi, figs. 

 187, 188) noticed in Ophelia neglecta an oval pore 

 opening into a goblet-shaped depression situated between 

 the two rami of nearly all the parapodia. Kiikenthal^ has 

 also figured a structure in a corresponding position in the 



' " Zur Anatomie und Histologic von Poiyoplit lialnnis pictus," 

 ' Arcliiv fill- iniicros. Anat.,' Band xxi, p. 791. Bonn, 1882. 



' "tjber das Nervensystem der Oplieliaceen," 'Jenaisclie Zeilsclir. f. 

 Naturw.,' Band xx, p. 510, and Taf. xxiii, tig. 24. Jena, 1887. 



