CLASS V. PISCES: ORDER 5. LEPTOCARDIA. 
483 
this tempting morsel is covered, soon crawl tliicldy 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 SYMBRANCHIDJE. 
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. 
Qenus PETROMYZON : 
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. 
Petromyzon, includes the Sea.-Lamprey, P. marimcs, 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 the 
table. There are other species. 
The American- Sea-Lamprey, 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 AMMOCCETES : Ammocoetes, includes the Plain Mud Lamprey, A. u7ucolor, common 
in the United States. It is popularly 
called the Lamper-Eel^ and is used 
for fish-bait. 
Genus MYXINE : Mixi ne^ in- 
cludes the Myxine of Europe, M. 
glutinosa of Linnaeus, Gastrohranchus 
ccecus of other authors, called Ghi- 
tinous Hag and Borer in England- 
The body is long and eel-like, and 
the skeleton is reduced to a mere 
cartilaginous tube. It pours out 
such an abundance of glutinous matter from the pores of the lateral fine, that the water in tha 
vases in which it is kept seems to be converted into jelly. 
THE EUROPEAN LAMPRBT. 
THE MTXINE. 
ORDER 5. LEPTOCARDIA. 
This includes a single small fish which rarely attains a length of over two inches, called the 
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 
