146 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



4. A sharply marked layer of diagonal muscles (PI. 12, fig. 79, 

 dm) lies just external to the main longitudinal layer. This oblique 

 layer is made up of two distinct sheets of fibers separated by a thin 

 layer of connective tissue. The parallel fibers of the outer sheet of 

 oblique muscles cross those of the inner sheet at nearly right angles, 

 and are thus most conducive to the strength of the body. The 

 oblique muscles thin out and disappear near the end of the eso- 

 phageal region. 



Besides the definite layers, the integument is penetrated by 

 numeroiis irregularly arranged fillers similar to those found in 

 Cakinei,la and Carinomella. 



5. In most regions of the body the main longitudinal muscular 

 layer presents a thickness greater than that of all the other muscular 

 layers combined (PI. 12, fig. 79; PI. 13, figs. 81, 82). Throughout 

 the intestinal region the outer circular layer becomes extremely thin, 

 while all the others except the longitudinal layer disappear entirely, 

 so that this latter represents almost the whole of the musculature. 

 Only in a limited portion of the esophageal region do the inner 

 circular muscles rival it in thickness. The lateral nerve cords lie 

 imbedded in this layer (PI. 13, figs. 81, 8'2), Avhich forms the inner- 

 most portion of the body walls proper. 



6. Internal to the longitiidinal muscles lies the gelatinous tissue, 

 or parenchyma, of the body cavity. This layer is but slightly devel- 

 oped in most parts of the body, and in the anterior esophageal 

 region is scarcely represented. Farther back it is more conspicuous, 

 but is never voluminous in this genus. 



7. The inner circular muscular layer (PI. 12, fig. 79 ; PL 13, fig. 

 81) can be followed continuously from the mouth to the anterior 

 end of the intestinal region. Its fibers are continuous with those 

 of the proboscis sheath, and, as stated below, it appears to originate 

 as a further development and prolongation of the proboscis sheath 

 musculature. Anteriorly it is even thinner than the outer circular 

 layei", but toward the jjosterior end of the esophageal region it 

 increases so greatly in massiveness that for a short distance it 

 exceeds in thickness the other muscular layers combined (PL 13, 

 fig. 82). Having reached its maximum development (near the 

 efferent nephridial ducts) it suddenly disappears entirely, its dorsal 

 portion remaining for a few sections as a semicircular arch above 

 the proboscis sheath. 



