270 PRACTICAL ZOOLOGY 



fourth year the larval lamprey undergoes a metamorphosis, dur- 

 ing which the structure and habits of the adult are acquired. 



Other Cyclostomes. — The other lampreys and the hagfishes 

 resemble the sea lamprey in most respects. They live in the 

 mud of the sea bottom and are of considerable economic impor- 

 tance because of their parasitic habits. All kinds of fish are at- 

 tacked by them, but principally shad, sturgeon, cod, mackerel, 

 and flounders. A hole is rasped through the body wall just 

 beneath the pectoral fins and the blood sucked out. Lampreys 

 are used as food by man, but they are not numerous enough to 

 be of any great value. 



The Brook Lamprey. — In many of the North American 

 brooks lives a very small brook lamprey, but since the adults 

 probably eat no food and the young live on minute animals and 

 plants, they are of no economic importance. However, if they 

 can be caught, they can be kept alive in the laboratory for a long 

 time and thus furnish excellent material for study. 



REFERENCES 



Fishes, by D. S. Jordan. — Henry Holt and Co., N. Y. City. 

 Bulletins of the U. S. Fish Commission. 



