26 EISEN 



Setchell, August lo, 1899, on the island of Unalaska. From notes 

 made by the collectors it appears that the specimens occur both under 

 stones and in sphagnum moss. The specimens from Metlakatla and 

 Lowe Inlet are not quite adult, so there will always remain some slight 

 doubt regarding their identity. Outwardly they resemble the type 

 specimens from the other localities. 



Characteristics. — With one exception, the largest JEnchytrccus 

 which has come under my notice resembles in size a veritable Allo- 

 lobophora, but possesses the general color of an Enchytrjeid. Form 

 and size of spermathecjE and sperm-funnels the most characteristic 

 features. 



DETAILED DESCRIPTION. 



Brain (fig. 4c). — Retractor muscles in three pairs; the two pos- 

 terior ones cover the whole posterior margin of the brain. 



Nephridia (fig. 4«) . — Nephridia large, the ducts are not very dis- 

 tinct in the specimens, probably the effect of the formalin preservative. 

 In the posterior lobe the duct seems to form a wide sinus (fig. 4a, ^). 

 At the base of the duct and close to the pore there is a widening of the 

 duct, forming a kind of urinary bladder, from which the duct is 

 branched and repeatedly coiled. No similar structure has come under 

 my observation in any other species. The form of the nephrostome is 

 illustrated by pi. 11, figs. 2 and 3, and requires no further description. 

 The nuclei of the nephridia in all my formalin material are so com- 

 pletely unstainable that they cannot be satisfactorily located. 



Atrium (p1. ii, fig. 4). — The structure of the atrium offers several 

 points of interest. The cells lining the lower part of the sperm-duct 

 are unusually narrow (p1. ii, figs, i, 5 and 6). Between them may 

 be seen the very thin ducts of the unicellular atrial glands (p1. ii, fig. 

 6) . These tips penetrate the lumen and hang down into it like cilia. 

 This protrusion of the glandular ducts is more evident on the surface 

 outside of, but close to, the spermiducal pore. Here the epithelial 

 cells are larger and, as they are not ciliated, the protruding ducts are 

 more readily observed. It is probable that a similar arrangement is 

 found in many species with atrial glands, and that only the smallness 

 of the specimens has prevented a correct observation. The tips of the 

 cells are readily mistaken for cilia or loose spermatozoa. In many 

 instances the epithelial cells lie so close together that the tips of the 

 ducts cannot be seen, except with the highest magnifications. In dif- 

 ferent parts of the lower portion of the sperm-ducts the epithelial cells 

 are of a somewhat different structure. Thus at a point marked ' xx ' 



