6. THE COF.LOM AND ITS DERIVATIVES - THE EXCRETORY SYSTEM 67 



Fig. 46. Transverse section of a male Lamellisabella zachsi in the postannular region of the metasoma. 

 be - ciliated band of the sperm sac; can - median coelomic canal; eg - gland cell of epidermis; 

 cph - sperm mother cell, lacking spermatozoa; cv - corpus cardiacum; eps ~ epithelium of sperm 

 sac; fm - muscle fibre; gt - pyriform gland; ml- longitudinal muscle layer; my - myocyte; 

 nd- dorsal nerve trunk; pgt - pore of pyriform gland; smt - somatopleura; sp - spermatozoa in the 

 sperm sac ; spl - splanchnopleura ; ts - spongy coelomic tissue ; vc - commissural vessels ; vd - dorsal 

 vessel; vv - ventral vessel, (i\fter Ivanov, 1960a.) 



all Pogonophora (Ivanov, 1955a, 1955b). They are, however, only discovered 

 with difficulty in the smaller species of Siboglinum and then only in well- 

 fixed material. This must be the reason why they were described in neither 

 S. weberi nor S. ekmani (Caullery, 1944; Jagersten, 1956). 



The coelomoducts are epithelial ciliated canals putting the protocoele into 

 communication with the external medium and hence appertaining to the 

 protosoma. They are thus evidently homologous with the proboscis pores of 

 the Hemichordata. 



Each coelomoduct consists of three parts: first a proximal canal, com- 

 municating with the coelom, then an excretory section, shaped like a back- 

 wardly pointing U-bend, and finally a distal discharge canal. This last 

 terminates in a thicker epidermal ampulla opening to the exterior by an 

 external pore. The proximal canals are attached to the coelomic sac apposite 

 to one another and run above the dorsal blood vessel (Pis. I, II, III). 



