RESPIRATION 



143 



within. Tubicolous polychaetes of the families Sabellariidae, Sabellidae and 

 Serpulidae possess extensive branchial crowns which are essentially filter- 

 feeding devices for extracting microscopic organisms from sea water 

 (Chapter 5). The pinnules of the crown (Fig. 5.5) are thin-walled structures, 



Fig. 4.3. Diagrammatic Representation of the Structure and 

 Disposition of Gill Lamellae in Teleosts 



(a). Gill filaments on two adjacent gill arches, (b). Enlarged view of one gill filament. 

 Large arrows indicate direction of water flow ; smaller arrows, course of blood through 

 arteries, arterioles and capillaries. (.From van Dam (30).) 



each of which contains an axial blood vessel; diffusion distances are about 

 1/u in Sabella. 



Extirpation experiments involving removal of the crown provide an 

 estimate of the amount of gaseous exchange occurring across the branchial 

 filaments. Loss of the crown depresses respiratory rate (oxygen consump- 



