PACIFIC COAST OLIGOCH.ETA. 131 



diverticula is distinct. The nuclei of the anterior pair are round while those of the 

 posterior pair are more oval, and the cells of the latter pair are not separated by dis- 

 tinct walls. They contain also numerous vacuoles or bladder-like bodies, some of 

 which deatch themselves from the main body of the organ. 



Figures 27 and 28 represent the anterior pair, 29 and 30 the posterior pair of 

 calciferous diverticula seen respectively under high and low power. The posterior 

 pairs only were found covered by chloragogen cells. These diffei'ences in structure I 

 also found in the calciferous diverticula of the following species: Benhamln pnlmi- 

 cola and rugo^d, and they [U'obably hold good with all the species of Benhamia. 



lyphlosole exists in somites xvii or xviii to xxii, and is greatly developed as 

 regards length, width and depth (figs. 7 and 14). It is widest and deepest in somite 

 xix, tapering or diminishing both anteriorly and posteriorly. In the following species 

 the typhlosole is much smaller. 



Spermathecai. The two pairs as usual in vii-viii and viii-ix. The form of the 

 spermatheca and its diverticula may be best understood from the flgui'es o4 and 35. 

 The pores come rather close together in a general groove below the ventral ganglion. 

 There is a muscular and a glandular part, and the spermatozoa were found as usual 

 principally in the diverticula. 



iSpermducis and rosettex. The only peculiarity of the spermducts is that they 

 are thickened in somites xviii, xvii and xvi. In xv the duct narrows, and continues 

 forward, with about half the thickness it possesses in the above posterior somites. The 

 thickening is due to an increase of a circular muscular layer (figs. 7, 11, 12, 13, 36, 

 37). The rosettes are in x, xi, as usual. 



Prostates. The usual two pairs are in xvii and xix. The lower part is long, 

 slender and muscular, while the upper thicker part is glandular. This glandular part 

 consists of only one layer of cells, covered by a thin epithelium. The glandular cells 

 are of different length, as shown in fig. 32. The muscular part consists mainly of a 

 thick layer of circular muscles (fig. 36), lined by a very thin layer of interior epi- 

 thelial cells (fig. 38). 



Penial seicr. A sac with two penial set* open jointly with each prostate. At 

 least one of the setae is sculptured as shown in the figures 31 and 33, with a number 

 of bristles, 12 or more. The smaller seta was broken in all the specimens, and I 

 could not ascertain if it was sculptured or not. 



NepJtridia. Benhamia nana belongs to a group in which the nephridia are 

 arranged in three rows on either side of the median line. There is not a diffuse 

 nephridic condition, but each nephridium is well developed, and upon the same 

 principle as the mega-nephridia of Acanthodrilus. Nephridia a. b. are ventral and 

 in front of setae 3 and 4, while the other nephridium c, is lateral and partly dorsal. 

 The 2)osterior nephridial ducts, from xvii to xviii, are superposed each on a large oval 

 sac of coelomic cells, while those in front of the male-pore are not furnished with any 

 coelomic mantle. Of the anterior nephridia those in the genital somites are some- 

 what smaller than those in the vicinity of the pharynx, the increase in size forward 

 being gradual. Blood capillaries are found in great numbers on all the nephridia, but 



Memoirs, Vol. II, 5. December U, 1895. 



