1901.] NATURAL SCIENCES OF rillLADELPIIIA. 705 



auf. Ueber ihre Natiir musste ich im Unklareu bleibeu ; niemals 

 beobachtete ich solche im Excretioiisgcfassliiinen selbst." 



The excretory duct, figs. 1, 45, Exc.d., is the small, thin-walled 

 tube that connects the main duct with the exterior. Its course is 

 in a plane at right angles to the plane of the main duct, and it 

 opens to the exterior just dorsal to the lateral nerve chord. Since 

 the excretory duct runs in a direct line to the epidermis with but 

 little turning or twisting, its length is merely the distance from the 

 main duct to the surface of the body wall. The cells composing 

 the wall are much lower than those of the main duct, and are 

 wider than high, the height being about .006 mm. Cilia are 

 borne on the ianer surface. No basement membrane is present. 

 The cells of the excretory duct meet those of the body epithelium 

 at the surface of the body, there being little or no invagination of 

 the epidermis. 



A good deal of evidently foreign matter from the exterior is 

 usually found in the excretory duct. 



9. The Alimentary System. — The alimentary canal of the 

 Heteronemerteans is usually divided into the following regions: 

 (1) The mouth; (2) the a^sophagus, or anterior intestine (" Vor. 

 derdarm," Biirger), a straight tube without lateral diverticula; (8) 

 the middle intestine (" Mitteldarm," Burger), with lateral out- 

 growths or cieca throughout its length; (4) the anal portion of the 

 intestine ("Enddarm"), a short region where the lateral cceca ar 

 no longer present, terminating in (5) the anal opening. Burger 

 (1895), p. 240, says: " Wir nennen den uugegliederten vorderen 

 Darmabschnitt Vorderdarm, den gegliederten, welcher der mittleren 

 und hinteren Korperregion characteristisch ist, den Mitteldarm. 

 Wir bezeichnen feruer am Mitteldarm den rohrenformigen Theil 

 als axiales Rohr, die peripheren Ausstiilpuugeu desselben als Darm- 

 taschen." 



According to Biirger, the (esophagus (Vorderdarm) has fre- 

 quently two regions, an antei'ior and a posterior, that differ histo- 

 logically from one another. In Garinella Biirger finds the epithelium 

 of the anterior part of the "Vorderdarm" very rich in gland 

 cells, while the posterior part consists mostly of supporting cells 

 with a few scattered gland cells; and in Cerebratulus marginatas 

 he finds the same differentiation of anterior and posterior parts? 

 45 



