CHAPTER XXI 
PHYLUM CHORDATA 
SUB-PHYLUM CRANIATA 
CLass CYCLOSTOMATA 
(Synonym, MARSIPOBRANCHII) 
Tue hag (A@yxine), the lamprey (Petromyzon), and a few 
others like them, differ in so many ways from Fishes, that 
they must be ranked in a distinct class. They represent an 
archaic type, whose interest has been enhanced by the 
discovery of Paleospondylus in the Old Red Sandstone. 
GENERAL CHARACTERS 
Unlike all higher Vertebrates (Gnathostomata), the 
Cyclostomata have round suctorial mouths, without distinctly 
developed jaws. They are also without paired fins and 
without scales. Their respiratory system consists of paired 
gill-pouches, to which the term Marsipobranch refers. The 
body is vermiform, the unpaired fins have no true fin-rays. 
In the extant forms the skeleton is wholly cartilaginous, and 
the notochord persists unconstricted. The nasal organ ts 
unpaired, there is no sympathetic nervous system, no conus 
arteriosus, no distinct pancreas, no spleen, no genital ducts, 
and the segmental duct persists as such. Their geographical 
distribution ts wide. 
First Type. M€dyxine—The Hag 
The glutinous hag (AZyxine glutinosa) is not uncommon 
off the coasts of Britain and Scandinavia, the Atlantic 
coast of America, etc. It lives in the mud at depths of 
