278 ELEMENTARY ZOOLOGY 



embryo. Lacking a distinct head, the lancelets are put 

 by some zoologists in a group called the Acrania, as 

 opposed to the Craniata, which includes all the other 

 vertebrates. Lancelets have been found in the North 

 Atlantic and Mediterranean, on the west coast of North 

 America, on the east coast of South America and on the 

 coasts of Japan, Australia, New Zealand, the East Indies 

 and Malayan Islands. The best-known members of the 

 group belong to the genus Amphioxiis. There are but 

 one to two other genera in the class. 



The lampreys and hag-fishes (Cyclostomata). The 

 next class of fish-like animals is that of the lampreys (fig. 



FlG. 113. A lamprey, Petromvzon martnus. (After Goode.) 



113) and hag-fishes, the Cyclostomata. The lampreys 

 and hags are easily distinguished from the true fishes by 

 their sucking mouth without jaws, their single median 

 nostril, tHeir eel-like shape and lack of lateral appendages 

 or paired fins. The hag-fishes (Myxine), which are 

 marine, attach themselves by means of a sucker-like mouth 

 to living fishes (the cod particularly), gradually scraping 

 and eating their way into the abdominal cavity of the fish. 

 These hags or "borers " "approach most nearly to the 

 condition of an internal parasite of any vertebrate. ' ' The 

 lampreys, or lamprey-eels as they are often called because 

 of their superficial resemblance to true eels, are both 

 marine and fresh-water in their habitat, and most of them 

 attach themselves to live fishes and suck their blood. 

 They also feed on Crustacea, insects, and worms. The 



