CHAPTER XXI. 



CLASS CYCLOSTOMATA. 



(Syn. Marsipobranchii.) 



The hag {Myxtne), the lamprey {Fetromyzon), and a few 

 others hke them, are so different from Fishes that they must 

 be ranked in a distinct class. They seem to represent an 

 old-fashioned type, whose interest has been enhanced by the 

 discovery of PalcRospondylus in the Old Red Sandstone. 



General Characters. — Unlike all higher Vertebrates 

 {Gnathostomata), the Cyclostoinata have round mouths without 

 distinctly developed jaws. They are also without paired fins 

 and without scales. Their respiratory system consists of 

 6-7 pairs of gill pouches, to which the ter7n A'larsipobranch 

 refers. In the extant forms the skeleton is wholly cartilaginous, 

 and the tiotochord persists uticonstricted. The " nostril" is 

 single, there is no sympathetic ttervous system, no conus 

 arteriosus, no pancreas, no spleen, and the segmental duct 

 is icnsplit. 



First Type. Alyxine — The Hag. 



The glutinous hag {Myxine glutinosa) is not uncommon 

 off the coast of Scotland, N. England, Scandinavia, &c., 

 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 it also enters and devours the 

 cod, &c., which have been caught on the hooks. According 

 to some reports, the hag also attacks free swimming fishes, 

 boring its way into them, but the evidence is not 

 satisfactory. Mr. J. T. Cunningham discovered that the 

 young animals are hermaphrodite, containing immature ova 



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