142 ZOOLOGY. 



The ovaries and male glands (the sexes being distinct) 

 are unpaired plates susj>ended from the back-bone, and have 

 no ducts, the eggs breaking through the walls of the ovary, 

 falling into the abdominal cavity and passing out of the 

 abdominal pore. The eggs of Myxine are very large in 

 proportion to the fish, enclosed in a horny shell, with a fila- 

 ment 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 

 bodies 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 marinas (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 toothless, and has other peculiarities. It is so strangely 

 unlike the adult that it was described as a different genus 

 (Ammocmtes). P. nigricans Lesueur is smaller, and oc- 

 curs in the lakes of New York and eastward. wbJle P. niger 

 Rafinesque is still smaller, and lives in the Western States. 



Class IV. — Pisces {Sharks, Rags, Sturgeons, Garpikes, 



and bony fishes). 



General Characters of Fishes. — "We now come to verte- 

 brates which have genuine jaw-bones and fins in pairs, and 



