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 coelomic epithelium. The cuticle (mit.) 

 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, v ~ 



(>fiid. ^ 



circ.tuu.i 



neph 



loity.mus- * 



let y 



ext.nepTv 



h rost 



sub.rLvcss 



Fig. 359. Lumbricus, transverse section of the middle region of the body. circ. mus. layer of 

 circular muscular fibres ; cwl. coslome ; cut. cuticle ; dors. v. dorsal vessel ; epid. epidermis ; 

 ext. neph. nephridiopore ; hep. layer of chloragen cells ; long. mus. longitudinal muscle ; 

 neph. ncphridium ; nephrost. nophrostome ; n. co. nerve-cord ; fct. setie ; sub. n. vess. sub- 

 neural vessel ; typh. typhldsole ; vent. v. 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 



