

PHYLUM ANNULATA 



419 



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

 V. an epidermis or derie^ epithelium, a 

 derm is, riniscultr 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 



FIR. 329. Lumbricus, 



setae, highly magnified. 



cells. Below 



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



dors, v 



cut 



hap 



set 



Lmmbricus, transverse section of the middle region of tin -.nvn. layer of 



circular muscular fibres; cosl. cr'!..niu; cut. cuti .epidermis; 



epli. afephridioporc ..<. longitudinal muscle; 



nephridium ; nep) 



. . ventral vessel. (After Marshall and Hurst. 1 ) 





.uscular fibres which make up the greater part of the thickness 

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



E E 2 





