250 



NEREID M. 



At the outer border of the dorsal muscles a strong series of fibres stretches obliquely 

 outward to interdigitate with the vertical. The oblique muscles slope downwards and 

 almost meet in the middle line, only a central pedicle connected with the nerve-area 

 above separating them. On each side of the median raphe dorsally is a strong fascicle 



vm 



Fig. 59. — Transverse section (diagrammatic) of the body-wall of Nereis diversicolor. bd., bv. Eespectively 

 dorsal and ventral divisions of the foot. d. Alimentary canal, d. m. Dorsal longitudinal muscles. 

 d. v. Dorsal blood-vessel. n. c. Nerve-cord. o. m. Oblique muscles. s. o. Segmental organ, v. m. 

 Ventral longitudinal muscles, v. v. Ventral blood-vessel; the main branches of this and of the dorsal 

 vessel are indicated. (After Goodrich and nature.) 



of fibres ensheathing the blood-vessel and decussating on the wall of the alimentary 

 canal beneath. The nerve-cords lie rather above the attachment of the oblique muscles 

 to the basement-tissue — a central pedicle occurring beneath. As a rule two large infero- 

 lateral neural canals (giant fibres) occur, with a median superiorly and occasionally two 

 smaller below the latter. The circulatory fluid in some contains hemoglobin. 1 Feet 



Pig. 60.— Diagrammatic sketch of the nephridium of Nereis diversicolor, O. F. M., with its canal, which is 

 divided into four regions, viz. 1—4. n. f. Nephridial funnel, n. p. Nephridiopore, (Goodrich.) 



somewhat complex with bifid dorsal lobe. Rarely is the dorsal lobe represented only bv 

 bristles. Bristles homo- and heterogomph. 



The nephridium of N. diversicolor (Fig. 60) consists of a compact mass, perforated by 

 a convoluted canal, which can be divided into several regions, and communicates with the 



1 Ray Lankester, ' Proc. Roy. Soc./ No. 140, p. 2, 1873. 



