456 



ZOOLOGY 



.SECT. 



The body- wall (Fig. 359) 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 sensory cells, 



dors i r 



typh 



neph 



wt.nepfo 



neph rost 



n.co 



cue/- set? 

 vend- v 



FIG. 359. Lumbricus, transverse section of tho middle region of the Ixiiy. dec. mt's. layer of 

 circular muscular fibres ; c<el. crelome ; cut. cuticle ; </o/-.<. r. dorsal vessel ; cpi<(. epidermis ; 

 ext. neph. nephridiopore ; hep. layer of chloragen cells ; lnn.it. m?<.s. longitudinal muscle ; 

 neph. nephridium ; nephrost. nephrostome ; n. co. nerve-cord ; n>t. seta; ; sub. n. vtss. sub- 

 neural vessel ; typh . typhlosole ; vent, i: ventral vessel. (After Marshall and Hurst.) 



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 muscular fibres which make up the 

 greater part of the thickness of the body-wall are arranged in two 

 principal sets a layer of circularly arranged fibres (circ. mus) 

 situated externally, immediately below the dermis and a layer of 

 longitudinally arranged fibres (long, mus) situated internally. 

 The circular layer is interrupted at all the intervals between 

 the segments ; the longitudinal layer is interrupted along 



