690 CHONDROPTERYGII. 



THIRD ORDER. CYCLOSTOMI, (Gr. xtxhog, kuklos, a circle ; or6,a, 

 stoma, a mouth.) 



The fishes of this order have already been referred to as hav- 

 ing sac or purse-shaped gills. These are fixed and open out- 

 wards by several apertures. The mouth consists of a circular 

 fleshy lip, with a cartilaginous ring supporting it; this peculiarity 

 gives name to the order. 



(36) Petromyzonida, (Gr. stone-suckers.) These have length- 

 ened, cylindrical, eel or worm-shaped bodies, destitute, both of 

 pectoral and ventral fins, but having foldings of skin above and 

 below, serving the purpose of dorsal, caudal and anal fins, 

 though without any supporting rays. 



The SEA LAMPREY, Petromyzon Americanus. In making its 

 furrow, preparatory to spawning, it uses its sucker-like mouth ; 

 with it separately removing stones of large size, and thus quickly 

 constructing a large furrow. It is from two to three feet in length. 



The MUD LAMPREYS, Ammocates, (Gr. sand-bedded,) include 

 several species which differ from the true Lampreys chiefly in 

 the form of the mouth, which is not suctorial, but composed by 

 the projecting upper lip, the lower one being transverse. 



These fish are found in large numbers, in sand or mud flats. 

 They are from three to four inches in length, varying in thick- 

 ness "from that of an earth worm to that of a swan's quill." 

 They are dug up from a depth of four or five inches below the 

 level of the water, and used as bait for fishes. 



The MYXINOIDS or Glutinous Hags, Myxynoidei, approach the 

 lowest form of the Vertebrates, and by Linnaeus and other writ- 

 ers, are classed with the Worms. These curious animals are 

 eel-shaped, and measure, when full grown, about a foot and a 

 half. The head is scarcely distinguishable from the body, and 

 is obliquely truncated in front, ending in a large round mouth, 

 the frame-work of which is a membranous, maxillary ring, fur- 

 nished above with a single tooth. The tongue has in each end 

 two rows of strong teeth. The Hag has no eyes ; the branchial 

 openings are two in number; the skin is covered with slime, 

 furnished from a row of pores on each side of the belly. An 

 obscure fin runs along the hinder portion of the back ; and is 

 continued round the compressed tail. The color is of a dark 

 bluish-brown above, and whitish beneath. 



The HAG or BORER, M. glutinosa, is found in the northern 

 seas of Europe. It does mischief by entering the mouths of 

 fishes caught in the lines of the fishermen and eating up all 

 the fleshy parts of their bodies, leaving only the skin and bones. 

 The name Borer is given to it, because, as is said, it pierces a 



