NOTES ON THE ANATOMY OF STERNASPIS. 235 



open farther forward in figs. 7 and 8. More forward still, the 

 membrane, which is for a considerable distance attached to the 

 tube by one edge, becomes quite free. The membrane and 

 the wall of the duct are ciliated on one surface only, and this 

 is continuous from one to the other. This description applies 

 to both sexes. 



As for the structure of the wall of the lobulated sac itself, 

 previous observers do not seem to have noticed that it also is 

 ciliated internally, — if not over its entire surface, at all events 

 along extensive tracts reaching up the lobes. Like the ducts, 

 it is covered on its outer surface with flat ca3lomic epithelium, 

 shown in fig. 10, a drawing of a fragment of the wall treated 

 with silver chloride and stained. In certain regions, separated 

 from the outer epithelium by a very thin connective-tissue 

 layer with a few muscular cells, is the ciliated internal lining, 

 cil. epith., formed of elongated cells with oval nuclei. Tiie 

 cilia are short and closely set along narrow longitudinal tracts 

 directed towards the base of the organ where the ducts come 

 off (fig. 9). The direction of the ciliary current is from the 

 tip of the lobes to the base, and down the ducts to the external 

 openings. The cilia on the membranous funnel, and on the 

 wall of the narrow canal leading from the coelom into the 

 genital sac, produce a current running inwards towards the 

 cavity of the sac. In this way, although the ducts and the 

 sac may be full of ova or spermatozoa, none are allowed to 

 stray into the body-cavity. 



The Nephridia. — These are two lobed sacs of a yellowish- 

 brown colour, situated in front of the genital organ (fig. 11). 

 Their general form and relations have been well described and 

 figured by llietsch (3)^. The main mass of each organ lies 

 closely applied to the oesophagus, and is connected with the 

 body- wall at the level of the intersegmental groove between 

 segments G and 7 (fig. 20) by a rapidly diminishing stalk, 

 with a narrow lumen, apparently ending blindly ; for, like 

 Vejdovsky and Rietsch, I failed to find any external opening. 



' " J'ai vainement clicrclic a Icur surface des entonnoirs vibrutiles, les 

 faisant communiquer avec la cavite geiicrale." — Ileitsch (3). 



