ON THE CCELOM, GENITAL DUOTS, AND NEPHRIDIA. 489 



Bergh, Wilson, Vejclovskv; and others, we have now a very 

 detailed history of the development of the nephridia in the 

 Oligochaetes. 



The observations of Hatschek,Wilsonj and Bergh do not coin- 

 cide in many particulars; but all these discrepancies have been 

 so admirably reconciled by Vejdovsky in his careful work on 

 Rhynchelmis and other forms (101), that we can, I think, be now 

 quite confident that we have a satisfactory account of the 

 embryology of these organs ; more especially since these results 

 have been in many respects amply confirmed by the researches 

 of Whitman, Bergh, and Burger on the Hirudinea. 



The development of the nephridium in Rhynchelmis has 

 been most carefully described by Vejdovsky (101). In the 

 first stage he figures it consists of a large cell (trichterzelle or 

 funnel-cell) within or on the posterior surface of the septum. 

 This '' funnel-cell " divides and gives off a string of small cells 

 behind, from which is developed the canal of the nephridium. A 

 large vacuole appears between the two cells formed from the 

 funnel-cell itself, in which a flame-like flagellum is developed. 

 Vacuoles now arise in the posterior string of cells, fuse together, 

 and form the lumen of the canal which communicates with the 

 end-chamber containing the " flarae^^ (figs. 6 and 25) . Finally 

 this chamber opens into the coelom, and the posterior loop joins 

 the skin ; a communication is established with the exterior by 

 means of a secondary invagination of the epidermis — the end- 

 vesicle. Quite similar is the development of the nephridium in 

 Stylaster and Tubifex (Vejdovsky, 100). 



Bergh (9 and 10) traced back the nephridia in Criodrilus and 

 Lumbricus to a large cell, the funnel-cell, lying close to the 

 epiblast and between each successive pair of solid mesoblastic 

 somites. When these become hollowed out, the funnel-cell 

 buds off posteriorly a chain of cells, the future canal of the 

 nephridium ; vacuoles appear in these cells, as in Rhynchelmis, 

 to form the lumen. Meanwhile the funnel-cell itself, which 

 has retained its large size, pushes through the mesoblast to 

 I'cach the coelomic cavity in the segment in front; here it divides, 

 acquires cilia, and becomes the funnel of the adult nephridium. 



