IV. 19 



HAG-FISHES 



123 



caught on lines (for instance, with a salted herring bait) the hook is 

 swallowed so deeply that it may be found near the anus! 



The gills are modified into pouches (6-14 in Bdellostoma, 6 in 



-5 



Fig. 82. Arrangement of gills in Bdellostoma and Myxine. 



1, tentacles; 2, wall of pharynx ; 3, branchial sac opened to show gill lamellae; 4, branchial 



duct; 5, branchial sac; 6, mouth; 7, common branchial aperture in Myxine. 



(From Kukenthal after Dean.) 



Myxine), opening by tubes into the pharynx, and to the exterior (Fig. 

 82). In Myxine all the tubes are joined and open by a single posterior 

 aperture on each side. Water enters at the nostril and is pumped back- 

 wards by a muscular velum through the gill chambers and out behind. 

 There is also a single posterior oesophago-cutaneous duct on the left 

 side, which is probably closed during normal respiration but is 

 opened to allow expulsion of large particles. If the nostril is closed 

 experimentally with a plug no water enters by the mouth or posterior 

 apertures but the fish survives well, presumably respiring through the 

 skin. 



