410 ZOOLOGY. 



ducts, the eggs breaking through the walls of the ovary, fall- 

 ing into the abdominal cavity and passing out of the abdom- 

 inal pore. The eggs of Myxine are very large in proportion 

 to the fish, enclosed in a horny shell, with a filament at each 

 end by which it may adhere to objects. 



The hag-fish is about a foot long and an inch thick, with 

 the head small, a median palatine tooth, and two comb-like 

 rows of teeth on the tongue. There is a single gill-opening 

 a long way behind the head ; there are large mucous or 

 slime-glands on the side of the body, for these fishes are 

 very slimy. The hag lives at considerable depths in the sea ; 

 we have dredged one at 114 fathoms in soft deep mud off 

 Cape Ann. It is often parasitic, attaching itself to the bod- 

 ies of fish, and has been found to have made its way into the 

 body-cavity of sturgeons and haddock. 



The lamprey lives both in fresh and salt water. The eggs 

 of the common lamprey, Petromyzon marinus (Linn.), are- 

 laid in early spring, the fish following the shad up the rivers, 

 and spawning in fresh water, seeking the sea in autumn ; 

 small individuals, from five to seven inches long, have been 

 seen by Dr. Abbott attached to the bellies of shad, sucking 

 the eggs out of the oviducts. 



The lamprey when six inches long is quite unlike the adult, 

 being blind, the eyes being concealed by the skin ; it is tooth- 

 less, and has other peculiarities. It is so strangely unlike the 

 adult that it was described as a different genus (Ammoccetes). 

 P. nigricans Lesueur is smaller, and occurs in the lakes of 

 New York and eastward, while P. niger Kafinesque is still 

 smaller, and lives in the Western States. 



CLASS III MARSIPOBRANCHT. 



Worm-like Vertebrates, without paired fins ; notocliord persistent ; a 

 single nasal sac, six or ten pairs of purse-like gill-sacs, no jaw-bones. 



Order 1. Hyperotetra. Nasal duct leading into the mouth. (Myxine.) 



Order 2. Hyperoartia. Nasal duct a blind sac, not connecting with 

 the mouth. (Petromyzon.) 



