100 



PART I. GENERAL ACCOUNT 



cut nd 



Fig. 67. Transverse section of a young female Siboglinum caulleryi a little behind the muscular 



diaphragm. 



eg - gland cell of epidermis; сое HI - coelom of metasoma; cut - cuticle; ep - epidermis; 



gon - oogonia; me - circular muscle fibre; mes - mesentery; ml - longitudinal muscle fibre; 



nd- dorsal nerve trunk; smt - somatopleura ; spl - splanchnopleura; vd - dorsal blood vessel; 



vv - ventral vessel. (After Ivanov, 1958a.) 



vessel is added to these two (Fig. 68). In Spirobrachia grandis, finally, there 

 are additional vessels in the lateral and medial walls, so that each ovary in 

 this species has five vessels. 



The cavity of the ovary is usually filled with tightly packed germ cells 

 (Fig. 66) and only in the hind part do the large oocytes come to lie more or 

 less free. The smallest oocytes are found in a particularly compact anterior 

 region of the gonad. As we move backwards along the ovary we find that the 

 germ cells increase in size and their cytoplasm becomes enriched with 

 yellowish granules and droplets of yolk and oil. The largest oocytes and ripe 

 eggs are found in the hindmost part of the gonad (Fig. 66). 



Pogonophora appear to lack follicle cells. 



The hind end of the ovary lies within the broad funnel of the proximal end 

 of the oviduct or even penetrates right into the oviduct proper. In the mature 

 female the wall of the ovary splits at this point and the ripe eggs tumble out 

 into the lumen of the genital duct (Fig. 66). 



The oviduct 

 As we have seen, there is no direct connexion between the ovaries and their 

 ducts. The latter represent a pair of epithelial U-shaped coelomoducts. The 

 internal broader limb of each of these tubes opens out into a funnel and may 



