90 MORPHOLOGY OF INVERTEBRATE TYPES 



the b bristles; two male genital pores on the fifteenth segment 

 between the bristles b and c; two nephridiopores or excretory 

 openings above the b bristles in every segment, except the an- 

 terior three and the last or anal segment; finally a single row of 

 dorsal pores in the mid dorsal line between the segments, be- 

 ginning with the seven-eight intersegmental line. These open- 

 ings connect the body cavity with the outside. 



Body wall. The body wall is composed of a cuticle, 

 hypodermis, circular muscles, longitudinal muscles and a thin 

 layer of parietal or somatic peritoneum. The cuticle which is a 

 product of the underlying hypodermis, is rather fine and pre- 

 sents when viewed from the surface a system of fine striation. 

 The lines intercross each other more or less at right angles and in 

 many points of intersection there are small pores. The under- 

 lying hypodermis consists of a single layer of columnal epithelium. 

 Between the common cells glandular and sensory cells are found. 

 In the clitellum the hypodermis is considerably thickened and 

 richly supplied with minute blood-vessels which run between the 

 cells. This region is, moreover, very rich in large gland cells 

 which become especially active during copulation and the for- 

 mation of the cocoon. The papillae of the twenty-sixth segment 

 contain in them capsulogenous glands producing the chief sub- 

 stance of which the cocoon is formed. Immediately under the 

 hypodermis is a heavy layer of circular muscles the function of 

 which is to elongate the body. Between the fibres of these 

 muscles pigment granules are found. To the inside of the cir- 

 cular muscles lies a still heavier layer of longitudinal muscles. 

 They form four bands, a right and left lateral band situated 

 between the lateral and ventral lines of bristles, a ventral band 

 occupying the space between the ventral lines and a much 

 broader dorsal band. The longitudinal muscles have a very 

 peculiar structure. They consist of a central lamella with a 

 series of parallel lamellae attached to the former on each side. 

 A transverse section of a longitudinal muscle has therefore the 

 appearance of a plume or feather. The function of the longitu- 



