2 OPHELIDLE. 



is the translucent cuticle with a thin layer of granular hypoderm beneath, the basement- 

 layer between this and the muscles being scarcely visible throughout the greater part of 

 the body-wall. The dorsal longitudinal muscles form a layer enveloping about three- 

 fourths of the body, each muscle being thinner toward the mid-dorsal line, where it meets 

 its fellow of the opposite side, and increasing in bulk as it approaches the oblique muscle, 

 above which a process passes a short distance inward. The oblique muscles are of 

 great strength, and slope inward and downward, to be attached below and at the side 

 of the nerve-cords, a few fibres even appearing above the flattened area in the posterior 

 region. This powerful muscle cuts off, as it were (in transverse section), the segment 

 containing the ventral longitudinal muscle with a portion of the coelom on each side, and 



4* 



.Xv-.m. 



-.v.m. 



Fig. 96. — Transverse section of the anterior third of Polyophthalmus pictus, Dujardin. 



as before. 



oc, ocelli. Other letters 



it is proportionally much less than the dorsal longitudinal muscle. The nerve-cords lie in 

 the middle line, and have only a thin basement-tissue, a very narrow layer of hypoderm, 

 and the cuticle externally. The cylindrical alimentary canal in the middle of the body 

 has externally a firm investment apparently containing some circular or elastic fibres, and 

 beneath is a finely granular glandular layer, a longitudinal muscular layer, and an inner 

 coat of columnar cells. Strong suspensory fibres fix it to the mid-dorsal line, and in the 

 mid-ventral line beneath is the ventral blood-vessel. 1 The ccelomic space in the example 

 examined is filled with large granular nucleated cells, apparently ova, and they also occupy 

 the spaces between the oblique and the ventral longitudinal muscles. A somewhat different 

 condition is observed in the section of an Ophelia, from the cruise of the 'Valorous,' 

 in which (Fig. 97) the oblique muscles form great sheets externally to the nerve-cords, 

 and cut off the ventral longitudinal muscles in the projecting region on each side. 



1 Claparede indeed held that the coelom was divided into three longitudinal chambers, as in the 

 Terebellidae. 



