TELETHUSjE. 



53 



of fasciculi, the dorsal and ventral muscles being clearly defined. The condition of the 

 musculature of the body -wall depends much on the preparation, for those with flaccid, 

 distended bodies present very different appearances from those in a vigorously contracted 

 condition. The former have a series of isolated muscular fasciculi inside the body-wall, 

 whilst in the latter the longitudinal muscles form more or less compact sheets. The 

 former taper dorsally, and are thickest a little above their lower end. 



crrv. 



o nv. . 



- clnv. 



--- vrrt. 



■-- cm. 



nt 

 Fig. 107. — Transverse section of Arenicola marina, L., behind the foregoing (106). 



The ventral longitudinal muscles are nearly of the same breadth throughout in 

 section, and have the origin of the oblique muscle as a boundary above, and the nerve- 

 cords in the mid-ventral line. 



Anteriorly in A. marina the nerve-cords which, though apparently single externally, 

 are double on section, lie in the mid- ventral region between the ventral longitudinal muscles, 



cm. 



Fig. 108.— Ventral wall of Arenicola marina, L., in contraction over nerve-cord, and with a Coccidian parasite (cp.) 



in the muscle. 



and form an ovoid area with a neural canal superiorly. Externally are the neurilemma, 

 hypoderm, and cuticle. The slender oblique muscles pass to their outer border for 

 insertion or fusion with the circular. The alimentary canal has a thin external invest- 

 ment, a few circular fibres, and numerous minute chloragogenous cells, which stain 

 deeply on its exterior. Within is a thick glandular layer which is thrown into numerous 

 folds. The blood-vessels along the gut have a thick coat of the glandular (chloragogenous) 

 tissue. The dorsal vessel has a much thinner coat of these cells than the others. Great 



