510 F. W. GAMBLE AND J. H. ASHWORTH. 



the case may be. They are not present on the first pair of 

 nephridia. A further account of these structures is given 

 below, p. 521. 



A. marina. — There are six pairs of nephridia opening on 

 the fourth to ninth chastigerous annuli. The smallest speci- 

 men of A. marina which we have obtained from the sand is 

 13*5 mm. in length (in spirit), but as it is somewhat contracted 

 its length when living would probably be about 1 7 mm. The 

 nephridia of this specimen, which are about "5 mm. long, have 

 already assumed the adult form. The funnel is of consider- 

 able size and has well-marked lips, the dorsal one bearing from 

 three to five short, blunt, conical elevations, which later on 

 become the large spatulate processes of the older nephridinm. 

 The secreting portion of the first nephridinm is a rather wide, 

 almost S-shaped tube; that of the following nephridia is much 

 wider and sac-like. There is a very rich vascular supply to 

 all parts of the nephridium. In a specimen 44 mm. long the 

 nephridia are about a millimetre in length. There is little 

 change from the condition described above, except that all 

 the parts are larger; the dorsal lip of the nephrostome bears 

 from four to seven small blunt conical processes, and the 

 secretory portion is larger and more sac-like. A nephridium 

 from this specimen is figured in our previous paper (1898, 

 pi. iv, fig. 16). 



Nephridia of large specimens may attain a length of 8 mm. 

 The funnel of such nephridia is large, and its dorsal lip bears 

 as many as thirty-two large spatulate processes, often branched 

 into two, three, or four distally. The processes are placed 

 slightly obliquely on the dorsal lip, i.e. a line drawn parallel to 

 their flat faces does not cut the lip of the nephridium at right 

 angles. The first pair of nephridia of A. marina is nnrepre- 

 sented in any other species of the genus. Their nephrostomes 

 are situated anterior to the third diaphragm, and the external 

 opening is on the fourth chretigerous annulus. In all other 

 species the first nephridium is situated in the segment pos- 

 terior to this one, with its external opening on the fifth 

 chsetigerous annulus. The first nephridium of other species 



