Page:Proceedings of the Royal Society of London Vol 69.djvu/367

Rh 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 excretory 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.