﻿412 PROCEEDIXGS OF THE NATIONAL MUSEUM vol. 102 



asymmetrical in size. Numerous specimens have the two dorsals 

 conspicuously smaller than the others, or one small and one large 

 dorsal. With the above condition, any one or two other tentacles may 

 be smaller than normal size. The figure of oral disk (pi. 30, fig. 1) 

 shows the primitive condition of four food grooves leading from mouth, 

 and how the original two dorsal tentacles were converted to four, 

 producing a doi-soventral asjmimetry. Just back of the upper flange 

 of upper lip is a conspicuous nuchal organ, which is broader than 

 long, with shallow longitudinal fm-rows. At its anterior margin is a 

 crescentic slit, between which and the lip flange is a ridge connecting 

 the bases of the two doi-sal tentacles. 



The skin papillae of the introvert are rather thick clavate, unequal, 

 the largest (0.135 mm. long) being at the base of the introvert, whence 

 they decrease in size toward the anterior smooth zone. Posterior to 

 the anus they very rapidly decrease in size to the dark brown, only 

 slightly convex, specks rather evenly and closely scattered over the 

 rest of the bod}". These are 0.04 to 0.07 mm. in diameter and, like the 

 papillae, have a central aperture (pi. 31, fig. 4.). 



The essential features of internal anatomy are shown in the figures. 

 The muscles have a satiny luster and the inner thin longitudinal layer 

 is transversely^ crinkled lil^e silk. Between the circulai" and longi- 

 tudinal layers are narrow bands of oblique fibers, which are more con- 

 spicuous in small than in full}" grown specimens. They do not extend 

 in front of the anus, are irregularly spaced, and not bilaterally sym- 

 metrical. In a small specimen 1 1 could be coimted on one side of the 

 body. Peebles and Fox (1933), refer to these as "the so-called veins." 

 The fibers are easily demonstrated. The two long retractors do not 

 join until a short distance behind the head. Rarely one of the re- 

 tractors is split in two. The distance between the posterior end of the 

 retractors and the end of the body varies; in well relaxed specimens 

 it is one-fourth the body length, or a little more. But in the big speci- 

 men from Point Conception the distance is a little over one-thhd the 

 body length. 



Characteristic are fixing muscles F^, F^, F^, F^ is attached to 

 ventral surface of esophagus, posterior to end of contractile vessel, and 

 passes backward to dorsal body wa]l. F- leaves the postesophageal 

 gut at the top of the spiral, while F^ anchors the ascending intestine 

 posterior to the coecum. But either F- or F^ is sometimes absent — 



Figure 87. — Demonstrating attachment of fixing muscles, or intestinal anchors, in three 

 species of Dendrostomum: A, Dendrostomum zostericolum. B-E, D .dyscritum: B, 

 Specimen from Crescent City, Calif.; C, specimen from Crescent City that lacks F' 

 and has abnormal attachment F^ (right nephridium is anchored to spindle muscle); 

 D, specimen from Pillar Point, San Mateo County, Calif. (F^ is displaced; F^ has two 

 strands); E, specimen from Monterey Bay (one strand of F^ sends two branches to 

 postesophagus. F, D. schmitii, paratype from Independencia Bay, Peru (F^ is divided 

 equally between postesophagus and ascending gut. 



