THE NEPHEIDIUM OP LUMBRICUS. 299 



specimen that first led me to a better understandiug of the real 

 nature of the funnel^ for no existing drawings or description 

 give any clue to the real mode of communication between the 

 coelom and the nephridial tube. 



I will now proceed to describe the true structure of the 

 nephrostome. 



If we follow the " narrow tube " forwards from the septum 

 to the funnel, we see in optical section the finely granular 

 wall on each side, with the nuclei of the component cells 

 alternately on this side and on that. Arrived at the centre of 

 the funnel, or thereabouts, the two walls suddenly diverge, 

 each bending outwards, and then sharply backwards nearly 

 parallel to its former course (fig. 4). The true " drain-pipe " 

 cells cease at this point of divergence. The backwardly 

 directed, or " centrifugal cells," as they may be termed, are 

 merely grooved ^ (fig. 32), but otherwise resemble the drain- 

 pipe cells in structure, being granular and ciliated. These 

 grooved or " gutter " cells, in reality, lie in a diff'erent plane 

 from the narrow tube, a higher plane when the funnel is 

 viewed from in front ; and they frequently hide the wall of the 

 tube, as is the case in fig. 5. 



After traversing a distance equal to about half the radius of 

 the funnel the gutter-cells suddenly cease, and become con- 

 tinuous with cells having quite a different appearance (fig. 4) ; 

 they are clearer and more distinctly marked off from one 

 another. They are, in fact, similar to the marginal cells, with 

 which they are continuous. The marginal cells are arranged 

 in such a way as to form what at first sight looks like a 

 circle, and has been figured as such ; but what in reality is a 

 horseshoe, the ends of which are bent inwards, the in-turned 

 ends being very close to one another. The cells forming these 

 ends may be called the '' centripetal '' marginal cells ; and, 

 as above mentioned, they meet the " centrifugal " gutter-cells 

 (fig. 4). 



The marginal cells are elongated, almost free from granules 



^ I. e. the lumen of the drain-pipe cell has enlarged ; the wall on one 

 side thins out till it parts, and the lumen is walled in only on one side. 



