PHYLCM ANNULATA 



419 



The body-wall (Fig. 330) consists of a 

 cuticle, an epidermis or deric epithelium, a 

 dermis, muscular layers with associated con- 

 nective-tissue, and, lining the inner surface, 

 a thin cellular membrane, the peritoneum or 

 ccelomic epithelium. The cuticle (cut.} is similar 

 to that of Nereis, and has a similar iridescent 

 lustre ; it is perforated by numerous minute 

 apertures. The epidermis consists, except on 

 the clitellum, of a single layer of cells 

 elongated in the vertical direction : many of 

 these cells have the character of unicellular 

 glands ; many others are nerve-cells, and are 

 connected by fine nerve-fibres with the nerve- 

 cord. On the clitellum the epidermis is 

 thickened, and blood-vessels extend between the cells. Below 

 the epidermis is a layer of connective-tissue, the dermis. The 



FIG. 329. Lumbricus, 

 setae, highly magnified. 



dors r 



typfi 



neph 



set 



sub.n.yess 



FIG. 330. Iiiimbricus, transverse section of the middle region of the body ; circ. mvs. layer of 

 circular muscular fibres ; cctl. ceelome ; cut. cuticle ; dors. r. dorsal vessel ; epid. epidermis ; 

 i..rt. ,ti:pk. uephridiopore ; hep. layer of chloragen cells ; long, irnts. longitudinal muscle ; 

 ixjih. nephridium ; ntplirost. nephrostome ; n. co. nerve cord; set. setae; sub. n. res*, sub- 

 neural vessel ; tiiph. typhlosole ; rent. r. ventral vessel. (After Marshall and Hurst.) 



muscular fibres which make up the greater part of the thickness 

 of the body-wall are arranged in two principal sets a layer of 



E E 2 ' 



