

On the E.irrctory Organs of Amphiostts. 351 



published a detailed description and figures of these segmental kid- 

 neys.* 



According to Boveri, each organ consists of a narrow ciliated tubule 

 opening on the one hand into the atrium at the top of a secondary 

 gill-bar, and on the other hand into the dorsal ccelom by one or more 

 funnels. Groups of peculiar cells, called " fadenzellen," are spread 

 round each funnel, attached to the coelomic wall. These cells send 

 each a long fine process passing towards the lip of the funnel across its 

 opening. 



During a visit to Naples this winter, I determined to re-examine 

 these structures in Amphioxus, with a view to comparing them with 

 the nephridia of certain Polychaete worms ; and I am now able to state 

 that the so-called " fadenzellen " are in reality typical wlenmytes, such 

 as I have described in the Glyceridse, Phyllodocida 1 , Alciopidse, and 

 Nephthyidse. f 



Hitherto the excretory cells, named solenocytes, have been known 

 to occur only at the inner extremity of nephridia, which end 

 blindly, having no direct communication with the cu-lom. Each 

 solenocyte consists of a cell-body and nucleus situated at the distal 

 free extremity of a delicate tube. The proximal end of the tube 

 pierces the wall of the nephridial canal, and opens into its lumen. A 

 single long flagellum, arising from the cell, works in the tube and pro- 

 jects into the canal. 



Now I find that the excretory organ of an adult Amphioxus is 

 formed of a ciliated tubule having an external but no internal open- 

 ing. It is more or less branched, and the branches bear innumerable 

 solenocytes with narrow thread-like tubes of remarkable length. At 

 the distal end of each tube is situated the cell-body and nucleus, and 

 inside it vibrates a flagellum which passes into the lumen of the 

 excretory canal. 



It may be concluded from those observations that, in their function 

 segmental arrangement, and detailed histological structure, the excre- 

 tory organs of Amphioxus are essentially identical with the nephridia 

 of certain Polychsete worms. 



* Boveri, Th., "Die Nierencanalchen lies Amphioxus," ' Zool. Jahrb.,' vol. 6, 

 1892. 



f Goodrich, E. S., " On the Nephridia of the Polyclueta," 'Quart. Jour. Micr. 

 Sci.,' Part 1, vol. 40, 1897 ; Part 2, vol. 41, 1898 ; Part 3, vol. 43, 1900. 



