CLASS V. PISCES: ORDER 5. LEPTOCARDIA. 



483 



this tempting morsel is covered, soon crawl thickly upon it, when the fish suddenly dives into the 

 water, leaving its prey struggling on the surface, from which it can pick them off at its leisure. 



THE SYMBRANCHIDJi:. 



In this family the branchial apertures, instead of being placed at the side of the head, as in the 

 two preceding families, unite to form a single opening, often divided by a longitudinal partition, 

 in the throat. They are all inhabitants of tropical countries, and live in fresh water. 



ORDER 4. CYCLOSTOMATA. 



This order contains a number of species of an elongated, cylindrical, and somewhat worm-like 

 character, of which the Lampreys are well-known examples. In respect to their skeletons 

 and some other parts of their organization, they are of the lowest rank in the scale of verte- 

 brated animals. 



Genus PETROMYZON: Petromyzon^ includes the Sea-Lamprey, P. marimis^ which is ovip- 

 arous, spawns late in the spring, and is 

 usually about two feet long. The color 

 is yellowish marked with brown. Like 

 the sharks and rays it is without an air- 

 bladder ; to prevent itself from being car- 

 ried about by currents of water, it fre- 

 quently attaches itself to stones by the 

 mouth, whence it is called Stone-sucker. 

 It feeds on soft animal substances, and is 

 found in the rivers of Europe not far from 

 the sea. It is highly esteemed for tho 

 table. There are other species. 



The American Sea-Lampuey, P. Ame- 



ricanus, resembles the preceding, though 



it is larger, and sometimes reaches three 



feet in length. It is taken in our bays and creeks in April; it ascends rivers and constructs 



conical heaps of stones where the spawn is deposited. The flesh is greatly relished. 



There are several species of river lamprey as well in Europe as America. 



Genus AMMOCQilTES : Ammocoetes, includes the Plain Mud Lamprey, A. unicolor, com.mon 



in the United States. It is popularly 

 called the Lamj)cr-Eel^ and is used 

 for fish-bait. 



Genus MYXINE : Mix'mc, in- 

 cludes the Myxine of Europe, M. 

 f/hi fino.sa of Linnicus, Gastrohranchus 

 ccEcus of other authors, called Glu^ 

 t'mous TliKj and Borer in England- 

 The body i,-. long and eel-like, and 

 the skeleton i:; reduced to a mere 

 cartilaginous tube. It pours out 

 such an abundance of glutinous matter from the pores of the lateral line, that the Avatcr in thd 

 vases in which it is kept seems to be converted into jelly. 



THE EUROPEAN LAMPREY. 



THE MTXINE. 



ORDER 5. LEPTOCAEDIA. 



This includes a single small fish which rarely attains a length of over two inches, called tho 

 Amphioxus lanceolatus. It is of a worm-like form, the vertebral column represented by a gelat- 

 inous cord, which supports the axis of the nervous system. The brain and spinal marrow appear 



