102 



PART I. GENERAL ACCOUNT 



The epithelium lies on a delicate basement membrane, and sparse muscle 

 fibres are scattered on the outside of the funnel. Where the funnel takes up 

 the whole width of the coelom its external surface, contiguous with the body 

 wall, lacks peritoneal epithelium, but where it becomes narrower and ceases 

 to occupy the whole cavity it is covered externally with a peritoneum. The 

 mesentery preserves its characteristic cellular elements in the region of the 

 funnels and rows of excretory cells are especially well developed here together 

 with folds of splanchnopleura containing small lateral blood vessels (Fig. 69). 

 The walls of the oviducts are very thin but rather rich in circular muscle 

 fibres. They consist of a very low epithelium which grows taller only near the 

 external genital aperture (Fig. 69). 



Fig. 69. Transverse section of a female Polybrachia annulata at the level of the genital apertures. 

 cv - corpus cardiacum ; epi - epithelium of funnel ; epo - peritoneal wall of ovary ; gp - genital 

 aperture; inf- lumen of funnel of coelomoduct; mes- mesentery; ml- longitudinal musculature; 

 nc - neurocord (giant nerve fibre); nd - dorsal nerve trunk; о - eggs; ov - ovary; ovd- oviduct; 

 spl - splanchnopleura ; vc - commissural blood vessel ; vd - dorsal vessel ; vv - ventral vessel. (After 

 Ivanov, 1958a.) 



