CHAPTER XX. 



CLASS CYCLOSTOMATA. 

 (Syn. Marsipobranchii.) 



The hag {Myxine), the lamprey {Petromyzon), and a few 

 others like them, are so different from Fishes that it seems 

 better to refer them to a distinct class. Unlike all higher 

 Vertebrates which have distinct jaws (Gnathostomata), the 

 hag and the lamprey (Cyclostomata) have round mouths 

 in connection with which ordinary jaws are not distinctly 

 developed. They are without paired fins and without scales ; 

 their respiratory system consists of 6-7 pairs of pouched 

 gills, to which the term Marsipobranch refers. The skeleton 

 remains wholly cartilaginous ; the notochord persists uncon- 

 stricted ; the " nostril " is single ; there is no conus arteriosus 

 in the heart ; no pancreas ; no spleen ; the segmental duct 

 is unsplit. 



First Type of Cyclostomata. 

 Myxine- — The Hag. 



The glutinous hag {Myxine glutimsa) is not uncommon 

 off the coast of Scotland, N. England, Scandinavia, etc., 

 living in the mud at depths of 40 to 300 fathoms. It often 

 lies buried with only the nostril protruding from the mud, or 

 it may swim about in search of prey. It eats the bait off the 

 fisherman's long lines, and is said also to devour the cods 

 and haddocks which have been caught on the hooks. 

 According to some reports, the hag also attacks living 



