46 



PART I. GENERAL ACCOUNT 



is often almost imperceptible, since it is usually wholly filled by a large 

 multicellular pyriform gland (Fig. 33). The epidermis of these papillae in 

 many Athecanephria contains large gland cells, with big vacuoles of trans- 

 parent secretion, concentrated at the base of the papillae on the medial side 

 (Fig. 33). The basement membrane of the papillae is joined to that of the 

 trunk. Beneath it lie muscle fibres running in various directions, including 

 around the papillae; a few muscle fibres cross the coelomic cavity of the 

 papilla covered in a sheath of peritoneal epithelium (Fig. 68). 



Fig. 33. Transverse section of Siboglinum caulleryi in the metameric region of the metasoma. 

 eg- ventral gland cells; со - dorsal ciliated band (cilia not drawn) ; сое III - coelom of the metasoma; 

 cpa - coelom of adhesive papilla ; dgt - duct of pyriform gland ; gt - pyriform gland ; mb - basement 

 membrane; mc - circular muscle fibres; mpa - muscle fibres of papilla; nl - lateral thickening of 

 dorsal nerve layer; ov - oocyte; per - peritoneum; pgt - pore of pyriform gland; pn - dorsal nerve 

 layer ; se - secretion in cell of pyriform gland ; vd - dorsal blood vessel ; vov - ovarian blood vessel ; 

 vv - ventral vessel. (After Ivanov, 1960a.) 



