198 



J. GRAHAM KERR. 



VI. The Post-anal Papilla and Nerves. 



A short distance behind the anus is a peculiar flap-like 

 structure, arising from the body-wall and bearing four papillae. 

 It varies much in form — sometimes being divided into two 

 distinct halves — sometimes continuous mesially — sometimes 

 thin and membranous — sometimes tumid and swollen. It is 

 covered by columnar epithelium, and filled with ordinary con- 

 nective tissue, sometimes with abundant jelly-like matrix. 



Fig. 5. 



Post-anal papilla with glands in the female. 



a, anus; p.a.p, post-anal papilla; g, openings of glands; n.g, nidamental gland; 

 p.c.v, pericardio-visceral aperture; neph, opening of kidney chamber. 



In the female, examination of this region with a hand-lens 

 shows the existence of a large number of apertures in the outer 

 skin. These, to the number of about 150, form a band about 

 0'5 mm. in width, curving gently forwards on either side of the 

 post-anal papilla, tapering off and terminating close to the 

 advehent vessel of the posterior gill. In section these openings 

 are seen to be the apertures of tubular ducts which pass 

 inwards perpendicular to the surface for some little distance 



