The Cyclostomes, or Lampreys 171 
land-locked and reduced in size by living in rivers only. Such 
land-locked marine lampreys (Petromyzon marinus unico'or) breed 
in Cayuga Lake and other lakes in New York. The marine forms 
reach a length of three feet. Smalle- lampreys of other genera 
six inches to eighteen inches in length remain all their lives in 
the rivers, ascending the little brooks in the spring, clinging to 
stones and clods of earth till their eggs are deposited. These 
are found throughout northern Europe, northern Asia, and 
the colder parts of North America, belonging to the genera 
Lampeira and Ichthyomyzon. Other and more aberrant genera 
from Chile and Australia are Geotria and Mordacia, the latter 
forming a distinct family, Mordaciide. In Geotria, a large and 
peculiar gular pouch is developed at the throat. In Macroph- 
thalmia chilensis from Chile the eyes are large and conspicuous. 
Food of Lampreys.—The lampreys feed on the blood and flesh 
of fishes. They attach themselves to the sides of the various 
species, rasp off the flesh with their teeth, sucking the blood 
till the fish weakens and dies. Preparations made by students 
of Professor Jacob Reighard in the University of Michigan show 
clearly that the lamprey stomach contains muscular tissue as well 
as the blood of fishes. The river species do a great deal of mis- 
an Bg 
Fig. 118.—Lamprey, Petromyzon marinus L. Wood’s Hole, Mass. 
chief, a fact which has been the subject of a valuable investiga- 
tion by Professor H. A. Surface, who has also considered the 
methods available for their destruction. The flesh of the lam- 
prey is wholesome, and the larger species, especially the great 
sea lamprey of the Atlantic, Petromyzon marinus, are valued as 
food. The small species, according to Prof. Gage, never feed on 
fishes. 
Metamorphosis of Lampreys.—All lampreys, so far as known, 
pass through a distinct metamorphosis. The young, known as 
the Ammocetes form, are slender, eyeless, and with the mouth 
