FORM OF NEPHRIDIA IN ARENICOLID.E. 



253 



which is attached by its outer surface to the oblique muscle, 

 forms the point of the arrow. The ventral edge of this lip is 

 set with from thirty to sixty ciliated plates which stand nearly 

 at right angles both to the plane of the lip and to its edge. A 

 loop of the blood vessel which traverses the dorsal lip runs up 

 into each plate. The ventral lip is bow-shaped and divided into 

 three segments like the handle and ends of a bow ; the convex- 

 ity of the bow turns toward the apex of the dorsal lip. The 

 opening of the nephrostome is a long narrow slit between the 

 base of the triangular dorsal lip and the bow-shaped ventral lip ; 

 the opening leads into the rapidly narrowing throat. The has- 

 tate funnel is held to the body by a short slender haft ; the body 

 of the nephridium, the glandular portion, is club-shaped ; the 

 funnel attaches to its side near the larger end, the axis of the 



FIG. 5. Dorsal view of a nephridium of A. marina, X *5- 



FIG. 6. Ventral view of the anterior end of the nephridium of Arenicola marina, 

 < 15. N. L. V., nephridial longitudinal blood vessel. O.M., oblique muscle. 



funnel being nearly at right angles to the longitudinal axis of the 

 body. The body of the nephridium joins the roughly spherical 

 bladder at the smaller end of the body, the handle of the club. 

 The bladder opens to the exterior on its peripheral side by a very 

 short duct leading to the nephridiopore. 



The nephridium of A. marina approaches, at times, quite nea 



