CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE 

 MUSEUM OF COMPARATIVE ZOOLOGV AT HARVARD COLLEGE, 

 UNDER THE DIRECTION OF E. L. MARK. — No. 129. 



CERTAIN SENSE ORGANS OF THE PROBOSCIS OF 

 THE POLYCHAETOUS ANNELID RHYNCHOBOLUS 



DIBRANCHIATUS. 



Bt Adele Oppenheimer. 



Presented by E. L. Mark, April 13, 1898. Received February 15, 1902. 



The proboscis of Rhynchobolus dibranchiatus was described by Elilers 

 ('(54-68, p. 670) as "short, thick, club-shaped, with small egg-shaped 

 papillae (compare Plate 1, Fig. 1), and was divided by him (p. 678) 

 into two parts, the " Rllsselrohre," or sheath of the proboscis, and the 

 " Kiefertrjiger," or bearer of the jaws. Before eversion the " Riissel- 

 rohre " is anterior to the " Kiefertrager," but when the proboscis is 

 everted (Fig. 1) the latter is anterior. The " Keifertriiger " may be 

 subdivided, as Ehlers suggested, into three regions, which in the non- 

 everted state are respectively anterior, middle, and posterior : (1) the 

 anterior has none of the small egg-shaped papillae ; (2) the middle 

 region is that supporting the four jaws ; and (3) the posterior is, as 

 a rule, not everted, it is the region of the four glands {gl.) of the 

 jaws and the remainder of the proboscis following the glands. The 

 boundary between " Kiefertrager " and " Rtisselrohre " is marked, ac- 

 cording to Ehlers, by the place of attachment to the proboscis of four 

 partial diaphragms, called by him " Lappen " (Fig. 1, Imn.). 



When cross sections of the everted proboscis are made in the region 

 of the four partial diaphragms (Fig. 2), one encounters in succession in 

 passing from the surface toward the centre (1) a cuticula {eta.) ; (2) an 

 epithelial layer {e'th.) ; (3) a connective-tissue layer {tis. co'nt.), in which 

 are embedded eighteen longitudinal nerves (n. Ig.), and a nerve plexus; 

 (4) a region composed of eighteen longitudinal muscles (mu. Ig.) ; (5) a 

 sheet of circular muscles {mu. crc.) ; (6) a fascia or peritoneum {pVtn.) 



