ORGANIZATION OF CERATOCEI'IIALE OSAWAI. 



249 



general structure of the organ is essentially the same as that in Nereis 

 diversicolor as described by Goodrich. 



Studied on sections, the funnel (fig. 4) or the preseptal portion of the 

 organ appears to have the wall composed of short, distinctly nucleated cells 

 arranged in double epithelial rows. This is apparently due to the fact 

 that the single-layered epitherial wall is reflected outwards and backwards 

 at the nephrostomal lip, so that the reflected marginal parts lie in contact 

 with the outside of the unreflected wall. The internal surface of the 

 funnel is provided with wavy cilia which are directed towards the body- 

 cavity and which are longest and most densely set on the nephrostomal 

 lip. 



The funnel passes behind gradually into the slender postseptal canal. 

 Here the wall consists of a single-layered epithelium (fig. 5.). The cilia 

 projecting into the lumen are posteriorly directed ; they grow ever shorter 

 and more sparse towards the nephridial mass. 



It has been stated by Goodrich* for Nereis diversicolor that the 

 funnel is attached to the free border of intersegmental septum, which 

 leaves a gap over the ventral longitudinal muscle, thus bringing the 

 ccelomic cavities of segments into direct communication with one another. 

 Probably the same condition obtains in CcratoccpJiale also ; however, I 

 have not been able to exactly determine the extent of septal gaps, nor the 

 relation between septa and segmental organs. Nevertheless, I have fully 

 convinced myself of the fact that the segmental organ has its nephrostome 

 located not in one and the same segment but in the segment preceding that 

 which contains the nephridial body and the nephridipore. 



The convoluted tube composing the nephridial body gradually nar- 

 rows its lumen towards the nephridiopore while the wall grows thicker in 

 inverse ratio. At the same time, cell-boundaries in the wall become less 

 and less distinct, and the nuclei larger. These show each a large nucleo- 

 lus. The ciliation in the lumen of the postseptal canal is continued for 

 some distance into the convoluted tube ; however, in the terminal parts of 



* Goodrich, — On a New Organ in the Lycoridea (Quart. Journ Mie. Sci. Vol. XXXIV. 189S.) 



