302 W. BLAXLAND BENHAM. 



(hence are clear in the living state)^ with an oval nucleus; 

 the cell boundaries are distinct, the outer free edge being 

 slightly rounded, and the whole of that surface of the cell 

 which is directed towards the funnel is ciliated. The centri- 

 petal marginals gradually decrease in size as the centre is 

 approached, and become cubical, while the nucleus becomes 

 round. 



The inner ends of the marginal cells do not reach to the 

 gutter-cells; and this space is usually figured, as by Goehlich 

 (20), by d'Udekem (31, pi. iii, fig. 6), by Howes (in the 'Bio- 

 logical Atlas '), and others, as being occupied by numerous 

 small rounded cells, considered as constituents of the funnel ; 

 these cells are, in truth, the " debris " ^ to which I have 

 referred above, and have no structural relation to the funnel. 



A very fortunate preparation shows the true structure of 

 the back of the funnel (fig. 4) ; the space between the central 

 ends of the marginal cells and the gutter-cells is occupied by 

 one large crescent-shaped cell, with a particularly large 

 oval nucleus containing a distinct nucleolus. This *' central" 

 cell is extremely difficult to see, for it is concealed by the 

 debris ; but having seen it in one funnel in which no debris 

 was present, I have been able to detect it in other cases in 

 which the debris was but slight; but generally it is completely 

 concealed. In sections it can readily be recognised, as 

 shown in fig. 7 (Ce.), which is the middle one of a series of 

 sections through a funnel in a young worm. 



The actual mouth of the funnel in communication between 

 the coelom and the uephridial tube is, therefore, placed 

 between the inner edge of the central cell on the one side (the 

 fine line a in fig. 4), and the outer edge of the grooved centri- 

 fugal cells of the other (the fine line h). The marginal cells 

 and the general shape of the funnel are secondary, and are no 

 doubt developed in order to influence by the ciliary current a 

 greater extent of the ccelom. As to the probable steps in the 



^ Beddard has figured such a mass of cells iu the funnel of Urochrcta (3, 

 pi. V, figs. 6 and 8 ; pi. xxiii, fig. 5), and has indicated it by "pg.-" he 

 believes them to be coelomic cells. 



