32 EISEN 



ciscanus^ of large nurse-cells, upon which are arranged the minute 

 spermatids in the shape of small globules scattered over the surface. 

 In the earliest stage there is no sign of tails. The nurse-cells (with 

 their charges) to the number of twelve or less are crowded together 

 into a little ball, which is surrounded by a distinct membrane. These 

 cysts or spermatophores begin to develop before they enter the sperm- 

 sacs, but the finishing stages of the spermatozoa are brought about in 

 the sperm -sacs. The cysts are found in the somites anterior to the 

 funnels, but no cysts were found either in the funnels or in the sper- 

 mathecse. In M. mirabilis^ as well as in J/, falciformis^ the cysts 

 were found in the funnels. While thus spermatophores are in no wise 

 characteristic of the genus, still they actually occur in several species. 



MESENCHYTIL^US OBSCURUS sp. nov. 



pi. VI, figs. I and 2; and text-figs. 12 and 13. 



Definition. — Length 23 mm., width 1.75 mm. Somites 78 to 91. 

 Setae sigmoid : laterals, 5, 4, 3, 3, 3, 4, 3, 3, 4, 3, XII, 3, XIII, 4, 

 4, 4, 4, 4, 4 (3, 3) ; ventrals, 10, 10, 10, 10, XIII, 7, 9, 8, 7, 6, 6, 6, 6, 

 (4,2). Head-pore at apex. Prostomium small, pointed. Clitellum 

 XII and XIII. Copulative papilla small. Septal glands IV to VI. 

 Dorsal vessel rises in XV. Intestine surrounded by chloragogen cells. 

 Spermathecse very large, with two diverticles near the base. The am- 

 pulla long and several times folded on itself ; walls very thin. Sperm- 

 ducts long, extending backward as far as XVII, about 8 times as long 

 as the funnels. Sperm-funnels slender, with a long recurved rim. 

 Atrial glands from 16 to 30, grafted on the atrium. Large penial 

 glands inside the penial bulb, opening close to the penis. Smaller 

 glandular cells inside the penis. Sperm-sacs large, extend backward 

 beyond IX, X, filling the coelom. Lymphocytes minute, ovoid. Ne- 

 phridia with three deep lobes. Color dark brown to yellowish brown. 



Locality. — St. Paul Island, Pribilof group, also Popof Island, 

 Alaska, July, 1S99, Prof. Trevor Kincaid. 



Characteristics. — This species is closely related to the California 

 species M. fuscus.^ but differs in its larger size, in its very dark color 

 due to masses of pigment, and in a larger number of atrial glands 

 opening into the atrium and through its very large but thin sperma- 

 theca, which fills the whole available space in the coelom. The num- 

 ber of setas is greater in M. obsctirus. 



DETAILED DESCRIPTION. 



Body-wall. — The layers of the body-wall thick, the general color 

 so dark that no interior organs can be made out except by dissecting. 



