SCALIBREGMKME. 



31 



The body-wall in Scaltbregma 1 is remarkable for its great muscularity, especially 

 posteriorly (Fig. 101), the thin cuticle covering a thick layer of hypoderm, as in Travisia, 

 and which rests on basement-tissue. Beneath is a thick circular coat, the outer fibres of 

 which pass downward to the ventral surface and a few meet across the middle line, over 

 the nerve-area, whilst others seem to pass into the oblique, thus making a muscular 

 commissure. The dorsal belt of these circular fibres is of great strength in this region, 

 and extends downward to the origin of the oblique with which some of its fibres join. 

 The rest of the fibres pass downward between each foot to form a thick layer in the 

 ventro-lateral area, some of the central fibres meeting, as already noted, over the nerve- 

 cords, whilst others appear to join the oblique of the opposite side. The oblique are 

 powerful muscles which bound the ventro-lateral areas internally, and enclose a space for 

 the ventral longitudinal muscles, which form a semicircular mass on each side. This 

 space, as in allied forms, encloses the segmental organs, which open externally at the 



Fig. 101. — Transverse section of the posterior region of Scalibregma inflatum, H. Rathke, from Lochmaddy. 



upper and outer border, and ova and other contents of the body-cavity enter it. The 

 dorsal longitudinal muscles are fused and form a thick arch over the coelom, the lower 

 border on each side being somewhat thinned as it approaches the oblique. The alimentary 

 canal in this part has a thin external wall of circular fibres, and apparently a few 

 longitudinal, whilst internally is a layer of basement-tissue bearing the thick glandular 

 coat. Its contents are sand-grains, mud, fine siliceous spicules and cellular debris. Ova 

 also occur in the cavities of the feet, the dorsal and ventral lobes of which contain 

 vermiform, striated, glandular tissue which stains deeply. The nerve-cords have a thick 

 granular and fibrillar layer, then the hypoderm and cuticle externally, whilst internally 

 are the circular fibres into which the oblique pass, and thus form a resistant boundary. 



Such a structure as the foregoing shows relationships with that of the Opheliidas in 

 respect to the spaces of the body-cavity and the muscular system, but it differs from that 

 family in the structure of the skin and in the form of the branchiae. 



In Eumenia Jeffreysii (Lijpobranchius of some) the cuticle and hypoderm agree with 

 those in Scalibregma, a very thin cuticle investing the thick granular hypoderm, which is 

 covered with papillse so as to make a tesselated surface. Beneath is a peculiar and deep 



1 'Proa Roy. Soc. Edinb./ Session 1876—7. 



